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For a start it depends on your focal ratio. An f5 scope has to be collimated much more carefully than an f10 scope. Near the optical axis there is a small zone where the image is pretty much perfect--a "sweet spot." You have to be sure that your eyepiece takes in this sweet spot, and that is what collimation is all about. If you miss the sweet spot, you get coma, and if badly out, astigmatism. The size of the sweet spot is given in this table.
f4--1.4mm
f4.5--2.0mm
f5--2.8mm
f6--4.8mm
f8--11mm
f10--22mm
f12--38mm
So for an f4, be very exact. For an f12, you need hardly bother.
Geoff
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