Can someone give me a summary of what all it can do?

OME is useful for firmware baselines and server configuration profiles, as well as hardware health info and launching the iDRAC console. It's good for alerting, and has the mobile integration too so you can get an alert email right to your phone.

SupportAssist can give you no insight into hardware health, but provides a way to track your open support cases, allows you to collect TSR logs to send to support without having to access the iDRAC console. It's more for handling and tracking case creation and sending logs to Dell. If you integrate it with TechDirect, you can get certified for self-dispatch. If an issue is detected for in-warranty parts during automated scans, you are prompted to confirm your shipping address for dispatching the replacement part.

You can also create multiple device groups and have different dispatch preferences for each of those groups - good if you have teams that are responsible for specific pools of servers. When an issue is detected or a case is created, the right contact will be reached out to. Overall, SupportAssist Enterprise's focus is more on interacting with support, creating cases automatically when there's an issue detected by SupportAssist, and getting parts out to you faster. 

It integrates with OME though so you won't have to do your server discovery again. I think if you plan to use it, it could save you a lot of time setting up cases on the phone with Dell. It is not a replacement for OME - it's pretty strictly focus on the support interaction and gives you very little insight as to the hardware health, firmware versions, etc at a glance.

Hope that helps!