Most important - disable ability to edit and remove posts (it seems it's implemented), and delete conversations (which are not answered). Don't let blocked user set some post as an answer on his question. Ability to move conversations across channels and change visibility should also be disabled - but for all users, I have explained in https://github.com/esotalk/esoTalk/issues/317
Disable avatar (or ability to change it) - otherwise user can set something not very friendly to the forum and administartor will have to delete it again and again.
Don't let suspended users recieve email notifications and follow: users, channels, conversations. In case he is blocked he has to go and open the site, it's too much functionality for banned one. He can also change his mail, star all conversations and channels and cause system to spend a lot of processor time to send this abuse traffic.
Don't show suspended user in online users sheet - not 100% sure but I think it make sense.