1. Rooting is like being given the Administrator account to a windows computer. Without it, you are limited in what you can do.
2. Having root access means having access to things in our system that your phone manufacturer doesn't really want you to have access to. This allows you to do things like overclock your processor, or delete system apps or "bloat" as we call it.
3. Both root methods I personally have used are so easy I find it impossible for anyone with half a brain to mess them up. That being said, while the root process is unlikely to harm your phone, what you do with your new found root access CAN.
At this point in time there is no SBF (a recovery option) for the Bionic available. So while you can root the device. If you delete the wrong system app and break something, your phone is going to be a nice paperweight for a while.