If you are one of the sheep (mon-thurs work crowd), then don't expect anything.

If you aren't one of the sheep, then you get exit row seats (usually) and occasional upgrades. The whole C+ thing is a mess. As a silver, I used to almost always be able to self-upgrade into C+ at 24 hours as the upgrades opened up C+ seats. The last few times I've traveled, Delta has locked down the seats and they ended up with standbys.

As a silver, I've gotten companion first class upgrades to SJU. YMMV