Assuming the leaks are much smaller than an exhaust hole, how does it affect temperature management?
For a drum lid, the gap is at the same height as the exhaust hole. I don't think the exhaust cares if it comes out of a hole you drilled or a small gap between the lid and the drum.
For either, I can't see a small gap doing much of anything because the pressure is greater inside the drum pushing the hot air out - not letting cold air. If the gap was located lower than the cooking grate height, it might be different.
White Sox UDS, Black UDS, Weber OTG and Performer, Orange Thermapen