Deleting from the Launcher removes it from your game, but it won't give you your disk space back.
Take the Sims3Packs you downloaded and put the ones you don't want aside. Then delete your DCCache folder. Then reinstall the downloads you want to keep. Because it is such a hassle, it's best to avoid installing anything with the Launcher unless you are completely certain you want it. To test something new in-game, back up your DCCache folder before installation to make the process less painful.