At STN & LGW it is not uncommon to receive an ATC, "expect late landing clearance, one to depart." If you are not lined up and ready to go as soon as the first landing has his tail bone over the vacated line ATC will not be best pleased; even more the one on short finals who has to GA. There is a huge difference at semi-quiet airfields where you can gently roll onto the strip for a smooth no rush rolling take off; and the maximising pushing tin during rush hour at others. ATC and the plots have to be sharp, listen out & think ahead, and be ready for anything at anytime.
Years ago, when I was at LHR for a short while, they seemed to have a smart sequence of SID's where the 1st went left, then next right etc. This gave adequate, but short enough spacing on the SID's.