As Time Machine uses up precious GB on my lean MBA I wonder if I actually need TM?
Given the statement above, you must be thinking about TimeMachine's mobile snapshots. This is a 'smart' feature recognizing that your data comes first so as your need for hard drive space expands, the amount of space TimeMachine gives to the mobile backups decreases. It can also be turned off using the terminal command found here.
Whether you use TimeMachine or some other software/system to backup your computer isn't important - that you have a plan is. Right now you have no backup plan - you have a recipe for a multi-hour cursing session as you reinstall your operating system, reinstall all your software, configure your system so you can access your gmail, dropbox and iTunes account, and then download some music and your entire DropBox. Then the cursing will start anew over the next serveral days as you slowly discover all the things that you didn't have backed up and should have.