There are all manner of reasons that start can't be given on some stands. In one case that i recall, the airport authority introduced a rule that aircraft had to be taken off stand and tugged to the end of the pier before starting because (when the wind was blowing in certain directions) exhaust fumes sometimes got into offices. Rumour had it that if the windows were closed as they were supposed to be in order for the air conditioning to work, that there was no problem but people in the offices often opened the windows for some reason. The result - tremendous inconvenience for crews, groundstaff and ATC and a distinct reduction in efficiency!