In the past Blackerrys had relativley small memories, this didn't matter that much at first but as the platforms grew, apps appeared, things slowed down.
So what you did with your leaked or official OS on your PC, was to manually edit your alx files, and remove your cod files you didn't want. Very time consuming but if you were a geek like me, very satisfying. Then a simple deletion of the Vendor.xml file and your away.
Nowadays there's so many shareware programmes, BBSAK/SHRINKAOS/Cracutil/BB Boss and even a cute app maxmem. They do it for you! Hats off to these guys, so please donate if the download asks. You cannot do any permanant damage (brick) your device by using these, the worst you would have to do is wipe your device and reload your operating software. So if you want to experiment do look at the tutorials here first, always back up your data.
So if you want to shrink, shrink away but remember, for more application space, and removing unwanted preloaded wallpapers etc. is the only real benefit
Still I will continue to do so