(Second and final entry in the semicolon series.)
Freer semicolon usage would help stem the promiscuous spread of artificial connectors, an assault on Concision. It would also contribute to Clarity by simplifying the representation of expectation neutrality, since and and but represent positive and negative expectancy of the following independent clause; but you may wonder when expectations are ever precisely neutral. The most important circumstance where a writer wants to represent the expectation as neutral occurs when the first clause expresses both a positive expectation and a negative expectation; the writer wants to avoid seeming to prejudge which is the stronger.
Oliver Wendell Holmes Jr. used the semicolon with great precision in his famous epigram, where the first clause expressed positive and negative expectations:
We do not inquire what the legislature meant; we ask only what the statute means.
Holmes renounces a purposivist approach to statutory interpretation but intends the implication to elicit surprise, greatest when a correlation obtains neither positively nor negatively. Holmes can create a sense of surprise because the renunciation carries two implications or expectancies: to interpret the text instead of interpreting the legislature's will or to renounce interpretation altogether. Logically, Holmes might have said instead: "We do not inquire what the legislature meant; we ask only what the legislature should have said."
A legal writer who uses semicolons with unusual effectiveness is Judge Richard A. Posner in The Economic Analysis of Law:
Generally, specific performance (ordering the party who breaks his contract to perform, on penalty of being held in contempt of court if he does not) will not be ordered as a remedy for breach of contract; the promisee will have to make do with damages, as suggested in the Holmes dictum quoted earlier.
(The Economic Analysis of Law, p. 117 [reference to Holmes coincidental].)
Here you can see the same pattern as in the quote from Holmes. The policy-of-denying-specific-performance clause activates two opposed expectancies: that another remedy will replace it or, alternatively, that none will; a different remedy or no remedy at all.