When Woody had his first dental (in London) he was about six and blood testing wasn't mentioned. His second dental was after I moved to Wales, when he was about 10 and the vet recommended blood testing, partly because of his age and also because he was fairly new to them (they'd seen him once before for an annual check and jabs).
They offered three levels of testing - basic, "older" cat and full - I went for the middle one. The dental plus tests still worked out cheaper than dental only in London!
... they specifically recommend it for neutering because it is likely to provide them with a healthy baseline on which they can gauge any future blood test results for that animal.
Makes sense if the kitten is in its forever home/at its permanent vet, where continuity of care is likely. (I've often thought it would be a good idea if people had basic tests done in their early twenties - blood pressure, blood sugar, cholesterol, etc - as a baseline for the future in working out what's "normal".)