The space required by the installation directories can be reduced dramatically if desired. Gzip all the .el files. Remove all the packages you’ll never want to use. Remove the TexInfo manuals. Remove the Info (and use just hardcopy versions of the manual). Remove most of the stuff in etc. Remove or gzip all the source code. Gzip or remove the C source code. Configure it so that copies are not made of the support lisp.
These are all Emacs Lisp source code and bytecompiled object code. You may safely gzip everything named *.el here. You may remove any package you don’t use. Nothing bad will happen if you delete a package that you do not use. You must be sure you do not use it though, so be conservative at first.
Any package with the possible exceptions of xemacs-base, and EFS are candidates for removal. Ask yourself, Do I ever want to use this package? If the answer is no, then it is a candidate for removal.
First, gzip all the .el files. Then go about package by package and start gzipping the .elc files. Then run SXEmacs and do whatever it is you normally do. If nothing bad happens, then remove the package. You can remove a package via the PUI interface (M-x pui-list-packages, then press d to mark the packages you wish to delete, and then x to delete them.
Another method is to do M-x package-get-delete-package.