Well in a shop setup it makes finding the true source of the leak a lot faster. Besides you can make a false find without it. Recently had a horizontal shaft engine leaking oil that appeared to be the crankshaft seal behind the flywheel. I almost pull the shroud and flywheel but instead went the UV dye route first. The oil leak wasn't even where it appeared to be. It was the oil fill cap leaking and the engine fan was sucking it up around the flywheel.Not seeing a reason to buy UV dye.
Do see several reasons to clean those oil/grit/dirt/grass lined/insulated cooling fins before you toss a valve other engine damage occurs.
Once the engine is CLEAN, that will help you locate the leak.