Generally short cut requests are greeted with "stand by" and I assume that this means a call to coordinate the request. I don't fully understand what goes on behind the scenes in ATC, and I am sure ATC don't fully understand my operational constraints, but I am convinced that short cuts are mostly made available to those who ask
It depends, sometimes you know where the point is, know where it is going to take you and know that the next sector are quite happy with the direct. Othertimes the point is fairly obscure and you've never heard of it, so you have to ask the next sector or unit wether its ok. Sometimes it might involve multi sector co-ordination which takes a while. Every sector will have points that they can send aircraft to the the next one that they know will not upset the next controller or cause a problem for them.
It will also (in the UK) depend on the mil. For example during the week the North Sea sector (S10/11) is restricted by danger area activity north of the airways and by training areas to the south so any directs are very limited. But at night and the weekends we get off-route status for all our traffic which means we can send aircraft all over europe to standard points for some traffic ie BEGOK for EDDF or GMH for EDDM or we juts ask MAAS and we get some wierd and wonderful ones. Half the problem we have is that the further away the point for the UK the less likely it is to be in the system so we don't know where its going to send you. Which can cause problems for separation. Sometimes directs are very useful i think its great watching three aircraft all at the same level going to different points fanning out on the radar.
Means we have more capacity because other levels are free.
Another point is that sometimes we want to send you to a fix and the pilot isn't looking far enough down the the FMS list of points and will keep telling us its not on their route when we know full well it is.
