This is my opinion and I will state it because personally I don't agree with what Barry has stated. If im wrong please let me know as its a fundamental error in my knowledge other wise and I have been sending alot of people up the bum track.
minor distortion in the mirror is absolutely detrimental to the proformance of the mirror in regards to photography! in visual it matters very little.
I have always had a fondess to hate laser collimators no matter how much you spend on them as you forget about what it is that your telescope is capturing.... light! Understand the light ray path and you will very quickly understand collimation!
I will pit my autocollimator and cheshire over a laser any day for accuracy in collimation and to point for newtonians even star testing! Why? well because seeing is rarely good enough to determine the airy rings, and its a long laborius process only to have the mirror move on you in transport. Sure it may have merrit in a observatory but not in the setup every night crowd.
I will how ever agree whole heartedly Barry that the point of collimation is to get every point of the mirror focusing on the imaging plane that is Square to the top of your focuser drawtube. But thats only 1 of 4 different errors.
of which you need to correct 2 out of 4 for perfect collimation.
The laser Erik owns corrects two but not at high accuracy.
Brendan