The bulk of the B & S engines on walk behinds had a fuel tank lower than the carb so it was not needed.
But nearly all other equipment with a tank above the carb was fitted with a tap.
Down here overhead tanks were the norm so every mower had a tap , either at the outlet or as Honda does as part of the carb .
In theory the float should stop gravity doing its worst but in reality most will eventually leak and theory is not going to come to your place & fix your mower for free.
I fit a tap to every mower, push or ride on that passes through the workshop, if for no other reason than it makes it quicker & cleaner to replace filters & clean the carbs.