Unless you need to compile a custom kernel with given options not already in the PCBSD*.i386 configs you probably don't need to worry about it.
I personally like compiling custom kernels under FreeBSD in so far as it does a bit of a stress test to compile it. The issue of boot speed etc resulting from one, well is a realm I butt my nose out of <_<
I would also recommend after you've read the handbook on the matter,
unless you have a I586 or I486 based CPU which is probably unlikely.