The parking lot is one the best tools in a negotiation. This is a place you can put issues that you are not ready to negotiate on yet until you see how the rest of the negotiations are going. You revisit the items in the parking lot at the end of the negotiations. If the negotiations are really working in your favor, then you are going to be more likely to give on these less important issues. But if the negotiations are not going so well for you, then you might negotiation much harder on some or all these parking lot issues.
I also use the parking lot for issues that both parties are stuck on and can’t seem to get over. Once you see where the negotiations are going, you (or the other party) may be more likely to give in on those items you were stuck on.
I always like to be the first to bring up the concept of the parking lot when I am negotiating. It has a funny way of giving you more control in the process. As you go through your points, you are the one who suggests, let’s put this in the parking lot and come back to it later.
Pro Tip: Before you even start the negotiations, have a few deal points that you think are good candidates for the parking lot.