Plumbers putty between tank and bowl

I suppose that this is a common problem, but while replacing a new overflow/flapper device in my toilet, and replacing the tank, one of the bolts which holds the tank on is seeping. This in itself is not too much of a concern, since the leak is not that great, but I was wondering, when I took the tank off of the bowl I noticed what looked like plumbers putty used as a sort of gasket (not sure if this is the correct term). I imagine that this is to keep the tank from rocking, but is this necassary, or just something that the contractor did to keep it quiet? I don't see it being related to my leak problem but I'm not really sure. With a gap, due to the putty, between the tank and the bowl I am afraid to tighten the bolts too tight.

PLUMBERS PUTTY?
No. Just don't do it.

There should be no plumbers putty between the tank and bowl.

Rubber washers or seals should be used.