Hm? I personally find them superfluous in 99% of cases.
If a sentence comprising of two other sentences is short, it would be read easier with a simple comma.
Long sentences are hard to read in general, and if you stick several loosely related clauses into one, you’d better separate them for the reader’s sake. Yes there still are cases, where you can feel that ‘halftone’ of a sentence partly related, but telling its own story – I am familiar with those yet from my native language, which quite possibly has adopted the semicolon from the Brits – but to write this way requires a certain condition between clauses and writer’s skill to see it, implement it and keep the whole clause legible.