I think one of the biggest mental benefits of Ares is being able to do multiple scenes at once, and async, because then I never feel like I am holding someone up. And people can feel freer to RP when they know they can set it and come back.
It seems like the MUSHing community has, by and large, stayed a similar community, and whereas a lot of us started our MU* career when were single without responsibilities, as we get older we start finding that we don't have six hours to spend roaming a grid and finding great pickup RP.
I always felt bad RPing with someone if I could not give them my full attention because I was working and prone to boss calls, or trying to accomplish something. Because I was keeping them from RPing with someone else.
With Ares, they can RP with that someone else and respond to me. And the same goes vice versa.
I think the other thing that is great about being able to easily do async is that there are amazing RPers that live half a world away that I would not be able to consistently interact with absent that.
Finally, I think the sheer versatility of the portal allows for you to do some really interesting things. Like have a game where you have a core character, but different versions of that character exist. You can use the same stats (or not stats if you aren't a stats game) and then just expand out from there with your variations.
Also, since it hasn't been mentioned yet, if you are a game with alts, being able to have ONE login in ONE place and connect all of your alts (if you want to, optionally) for the purposes of pages, channels, and RPing? Huge plus if you want to keep track of things.
Honestly, it's going to be a struggle to convince me to go to any non-Ares game at this point because I have simply gotten too used to the conveniences.