Removing RewriteBase / from my htacess has sped up my site which is still working correctly. Is it really required and what is it for?
'RewriteBase /' is not needed. RewriteBase allows you to change your internal directory structure to something other than what a browser sees. IE: If all your files are in 'http://mydomain.com/site', but you wanted 'http://mydomain.com' to be the path browsers see, you would use a
RewriteBase /site and apache's mod_rewrite would happily add that substitution for you.
RewriteBase / is not necessary.