connecting along dame
An attack on a weak group can force you to connect (to a strong group). If you have to walk on dame points by doing this, while the opponent makes territory, the opponent may have gotten sufficient profit out of the attack.
Worse is when you connect to something so weak that together the two groups are a little stronger but also much heavier.
Even worse is connecting groups along dame points, which are already safe. This often happens in the endgame. Virtual connections which have long been important, are threatened to be cut, but in these later stages both ends already have two eyes and no points are lost by the cut. Connecting makes 0 points in gote.