What Martin says on this is true for UNIX systems, however
PCs generally have smaller slower hard disks and less efficient
disk handling in the OS. Accordingly, I have found it quite useful
to strip the libraries of comments and spurious space. I have a
small PERL program to do this if anyone wants it.
There is an additional benefit of the load and dump technique
used by EMACS and TeX, which is that, with a little care, most of
the loaded libraries can be marked as 'pure' code, never altered
by the program. This enables multiple users to share a single
copy in memory.