should be on to be se friendly,just makes pages se friendly instead of something like /webdirectories.php?=12 so on and on turns it to /Web-Directories or something like that, but its good nothing bad
Will it give any 404 error if somebody do it now.. Suppose I am running my directory since months, got few backlinks for my directory targetting category pages like www....com/c=1.php etc.. and changing it now via url rewrite to www...com/directories - will it give not found error ?
I think it will not give any error as Search engine indexes all your pages via the main page index.php