What kind of improvements do you get by rooting?
- Far quicker updates to firmware and android versions.
- And these updates will still be produced long after HTC stop updating our phone
- If a firmware release is buggy, it gets fixed in days, not months
- Your phone becomes
far more customisable. Off the top of my head, you have the option of HTC Sesne, MIUI or vanilla android UI. You can theme these UIs. Many roms like cyanogen add a tonne of new settings to the phone
- Firmware is tweaked and improved to run faster + smoother
- On top of that you can overclock your processor, if you want
- You can also undervolt your processor, reducing the power it uses for the same amount of work.
- Access to root only apps
- Probably more that don't spring immediately to mind.
Now there are of course downsides:
- This is not the option for people who like stuff to just work. You will spend a lot of time customising your phone and will update your firmware far more often than before. (There are lots of root only backup programs that save you a lot of time and automate the process, but still).
- Your warranty is void should you have to return the phone rooted. However, it is possible to return the phone to stock should you need to return it.
- It is possible to brick your phone entirely, turning it into an expensive paperweight. This is almost entirely caused by people rushing into things without reading up on it, but it has been known for a developers mistake to brick handsets before. In those cases it seems that HTC will still repair it (since they can't turn it on to check), but it's still a risk; they are perfectly within their rights to claim your warranty is void.
I'm definitely pro-root (I had previously rooted my Hero and so I rooted my DHD day one

), but you should be aware of both sides of the argument.