Yes! IME, it matters greatly. With my latest wall decoupling system, I can actually hear if the tt gets off level. A wall system, no matter how great is dependent upon the expansion/contraction of the studs. I use a 10" Bosch level. A longer level will give a more accurate reading.
Generally, for a tt with a non-inverting bearing, one does a final level on the platter, on an inverting bearing, the final level is on the plinth.
Generally, for a tt with a non-inverting bearing, one does a final level on the platter, on an inverting bearing, the final level is on the plinth.