If you don't know what you can do with them, why are you thinking of buying one?

Read the stickies, use Google. You'll soon find what you're looking for.

Do more research before you think about buying one. youtube some videos about jtags and their uses

YoTrashtalkings wrote So, I'm thinking about buying a JTAG what can you do all do with them?

If you cant answer this yourself, than do some more research before buying one. End of story

There are many things you can do with a Jtag/RGH

- Run homebrew
- Have access to features that non-Jtag/RGH users would not
- Play backed-up/downloaded games
- Get Downloadable Content for free
- Mod most games a lot more than you can do with an ISO/USB
- You can make money if you use the resources right

The list is almost endless...
You may want to look into buying an RGH instead as RGH's are easier to find and are more reliable in many aspects.
If you do buy a modded console, you must be aware of the risks/dangers; Flashing a bad NAND, Bricking the xbox, and NEVER, NEVER update the dashboard when prompted on the console or you will blow the EFUSE's and it will never boot again.

Modding is very enjoyable, but quite costly if you plan to go online on the console.
I suggest reading up on do's and don'ts with a modded console and in no time, you'll have all the knowledge you need