I'm sure there were a few threads early on in the Dream forum about why people should bother rooting - the benefits and such. Might be worth a specific search in there for threads like Why should I bother rooting or what are the benefits of having root? etc.
Here's how I understand it -
Seems to me Root was more important on the Dream, because it meant you could do stuff like putting a different ROM on with extras like Soft Keyboard and Latitude, and also move stuff like caches to SD Card, and more recently, move apps themselves to SD Card. This was damned near essential, due to the much smaller space on the handset for apps etc (In my experience it was about 75MB after a wipe - tiny) and the fact that the Market Cache wasn't easily clearable. Without Root, you couldn't alter those annoying things even if you had the knowhow, because you were "locked out" of changing the main ROM. So Root allowed you the freedom to modify stuff.
Other things you can do if you have root include ADB push stuff, so you can alter small parts of the system folder to suit you - like adding languages or keyboards or modified boot images etc. You can do Nandroid back ups of your whole system including installed apps, so that you can restore the apps after a wipe, or backup a ROM that works so that you can go back to it if you load one that doesn't work. Also you can install custom themes to make your fone look less generic. I believe there are ways to get tethering to work (Using the modem/internet access on the device/fone to link up via bluetooth with a laptop or netbook and surf as if you have a USB Dongle.
Some of the reasons I rooted my G1 are mute now or don't apply to the Magic
eg - More space on the magic for apps so I don't need to make more room by putting caches on SD or moving apps to SD
Cupcake update has soft keyboard anyway, and latitude
Also we now seem to be able to clear the caches for most apps via the Apps Manager, so stuff like Market and Browser doesn't grow with use and get out of hand.
Home app replacements are far more stable and are great for having different themes so no need to alter the main themes using root.
So, I haven't rooted my Ion/Magic as yet. If and when theres a really stable ROM without gliches I might go for it, but no real need for me as of yet so not gonna mess. I'm sure other folks can give you more reasons to either go for root, or leave it as it is.
G1 - Google Ion - HTC Hero - Milestone - Nexus One - Desire Z - Galaxy S2 - Galaxy S3 - Samsung Galaxy 4 currently using Omega Rom
Twitter : @daized
My Amazon Author's Profile