[kbolino]

One of the major optimizations is to pass function arguments in registers instead of on the stack. These registers might preserve their original values by the time you unwind the stack, but in many cases, probably won't. Preserving those values would lead to fewer available registers and/or more frequent register saving, which would create at least some overhead, even if you don't ever inspect it.

There are probably lots of situations where it's worth it, though.