Recessed light wiring
You can run from one can to another in any way that makes sense. Typically this would be done to minimize the cable length. It is easier to run parallel to the trusses and minimize truss crossings (this depends somewhat on your insulation). If you have a single line of recessed can lights this should be an easy run from switch to end, but if you have a grid like I did you should plan the cable route in an S or U shaped pattern.

You can run Romex through fiberglass insulation but you should minimize the runs &quot;through&quot; insulation if possible i.e. don't cut a slot in the insulation and wrap it around the Romex. Poke holes if necessary, insert through it, run over the top or around the side of the insulation. More than Romex interacting with insulation though, be aware of installation safety instructions with the can lights, most of which require minimum clearance between the can and any insulation in the ceiling. LEDs which don't heat up the metal housing quite as much have lower clearance requirements, but be sure to check.

Ecnerwal answered succinctly in a comment:



You don't have to staple when retrofitting in existing construction
where it would be onerously destructive to tear things up so you can
attach cables. NEC 300.4, D, Exception 2