Yea the game will have to re-install from the disc but not sure if it will download patches if you don't delete the updates.
Just remember if you delete some files you may find that your studio will be empty so you will loose any saved sims, houses, clothing and any rewards/challenges you've unlocked/completed.
Your actual game save files will still work though so you could easy unlock/complete some of the rewards and challenges again if you load them and play them for a sim day or 2 and also save your sims or houses to the studio should you want them back.