If I uninstall or delete a Steam game on my computer, will it give me back the space/usage it took to download?
Deleting the local files of a game (via right-clicking a game and selecting 'Delete Local Content) will free up all the space that that game is using on your hard drive. For large games like TF2 this can be more than 15 GB.
However, it will not free up any internet data that it took to download (if that is what you are referencing to in
the space/usage it took to download). If your data cap has run out, I suggest you contact your ISP (internet service provider) or look on their website to purchase more data.
Please note that deleting some games will delete your savedata, it depends on the game. If your savegames are stored in your Users folder (My Documents etc) they should be fine, otherwise, it would be a good idea to check.