The ampersand should be avoided in body copy. It disrupts the flow of the text and produces an unsightly type colour. Its use in this manner is pleasantly absent in any professionally written and designed publication or correspondence. Needless to say, indiscriminately mixing “&” with “and” is an even worse offence.
In fact, in most prose, the ampersand is best avoided except in certain standard cases, such as in company names (e.g. H&FJ, Secker & Warburg, Walrus & Barnacles).
Due to the wonders of modern computing technology, the removal of offending ampersands in any particular document is now a trivial matter. However, this can in no sense be viewed as license to cultivate poor habits in the first place. Every find and replace takes time and involves risk. Even the loss of a few seconds might become critical in a tightly-managed workflow, and the accidental omission of an ampersand in any one of the few instances where its use is not only legitimate but also necessary could lead to serious consequences.
Further arguments against the indiscriminate use of the ampersand:
You may have convinced yourself that, since the ampersand consists of just one character, and “and” consists of three, that typing the ampersand represents a more efficient use of the motor movements of your fingers than depressing all three letters on your keyboard in repetitive, RSI-inducing sequence. You are greatly mistaken. To reach the ampersand requires an extremely awkward movement of the right index finger, which must stretch all the way up to the first row of the keyboard in a QWERTY layout. Furthermore, you are required to hold down the shift key simultaneously. On the other hand, since each letter of “and” resides within easy range of your fingers, this word can be typed extremely rapidly and easily. Therefore, in the time it takes your index finger to reach up for the ampersand, and while simultaneously wasting motor energy holding down the shift key, you could have already completed the next word of your sentence if you had simply written “and.”
Punctuation is relatively fluid in English. “Within the framework of a few basic rules (fewer still in fiction), an author's choice of punctuation is an ingredient of style as personal as his or her choice of words” (Oxford Style Manual, 112). However, this does not mean there are not definite instances of misuse.
Wrong use of punctuation here is not only jarring - it can also lead to misreading.
Nonrestrictive relative clauses are parenthetic, as are similar clauses introduced by conjunctions indicating time or place. Commas are therefore needed. A nonrestrictive clause is one that does not serve to identify or define the antecedent noun.
The audience, which had at first been indifferent, became more interested.
In 1769, when Napoleon was born, Corsica had but recently been acquired by France.
Neither Stowey, where Coleridge wrote The Rime of the Ancient Mariner, is a few miles from Bridgewater.
In these sentences, the clauses introduced by which, when, and where are nonrestrictive; they do not limit or define, they merely add something. In the first example, the clause introduced by which does not serve to which of several possibile audiences is meant; the reader presumably knows that already. The clause adds, parenthetically, a statement supplementing that in the main clause. Each of the three sentences is a combination of two statements that might have been made independently.
The audience was at first indifferent. Later it became more and more interested.
Napoleon was born in 1769. At that time Corsica had but recently been acquired by France.
Coleridge wrote The Rime of the Ancient Mariner at Nether Stowey. Nether Stowey is a few miles from Bridgewater.
Restrictive clauses, by contrast, are not parenthetic and are not set off by commas. Thus,
People who live in glass houses shouldn't throw stones.
Here the clause introduced by who does serve to tell which people are meant; the sentence, unlike the sentences above, cannot be split into two independent statements. The same principle of comma use applies to participial phrases and to appositives.
People sitting in the rear couldn't hear. (restrictive)
Uncle Bert, being slightly deaf, moved forward. (nonrestrictive)
My cousin Bob is a talented harpist. (restrictive)
Our oldest daughter, Mary, sings. (nonrestrictive)
When the main clause of a sentence is preceded by a phrase or a subordinate clause, use a comma to set off these elements.
Partly by hard fighting, partly by diplomatic skill, they enlarged their dominions to the east and rose to royal rank with the possession of Sicily.
[Strunk & White, The Elements of Style, 3-5]
A commenting [nonrestrictive] clause should be within commas; a defining [restrictive] one should not. This is not an arbitrary rule; it is a utilitarian one. If you do not observe it, you may fail to make your meaning clear, or you may even say something different from what you intend.…
I have made enquiries, and find that the clerk, who dealt with your enquiry, recorded the name of the firm incorrectly.
The relative clause here is a defining one. The comma turns it into a commenting one and implies that the writer has only one clerk. The truth is that one of several is being singled out; and this is made clear if the commas after clerk and enquiry are omitted.
The same mistake is made in:
The Ministry issues permits to employing authorities to enable foreigners to land in this country for the purpose of taking up employment, for which British subjects are not available.
The grammatical implication of this is that employment in general is not a thing for which British subjects are available.
An instruction book called “Pre-aircrew English,” supplied during the war to airmen in training in a Commonwealth country, contained an encouragement to its readers to “smarten up their English.” This ended:
Pilots, whose minds are dull, do not usually live long.
The commas convert a truism into an insult.
[Gowers, The Complete Plain Words, 244-46]