Exit criteria place a segment node after the entry point and all Wait nodes. Depending on the complexity of your program, this could cause heavy load. In such cases you could consider using a filter switch before the channel nodes to exclude contacts.
Including exit criteria in your program can also affect performance. If you specify a segment as an exit criterion, that will essentially insert a segment node after every entry point and every timer. So when you have exit criteria defined you should only count on 300 contacts/minute to pass through the entry nodes and timer nodes.