@Dziki94 Honestly I've seen no reason to use the "set up" traps, myself. I play the ranger as (crazy thought) a RANGED class. Charging in close enough to set up and make use of a "proximity-fuse" trap is completely contrary to how a ranged class should work. At least in my opinion. I did invest in the Grenades, though. Those can be useful, especially if you get swarmed by fast mobs or run out of PP and need to recover it quickly. I toss them both during stunned/DPS phases as well if I'm close enough. Although honestly I've more or less forgotten to use them quite frequently since returning to Ranger after cycling through several other classes to level them up (still considering whether I might drop Ranger for the more nimble Hero with a focus on TMGs to maintain ranged combat options).
But yea, other than throwing the occasional grenade when I play ranger I play the long-range game. I hang back as far as I can without losing the ability to lock onto a target. I stick with Steady Shot and Slide Burst (for evasion/re positioning) when using rifle and Divine for the Launcher, with Cosmic Breaker set aside for stun/DPS stages, and THAT is the only time I "break class" and get in close. CB is useless at long or even medium range, so when there's an opening I rush into "I can smell what you had for dinner last night" range, pop a CB, dive-shot to recover some PP and break the animation lock at which point the CB round has made contact (you don't want to fire another one before the previous one hits or it will cancel it out) and I launch another, followed by another dive-shot. Rinse, repeat, run like hell when the boss gets back up, then hop into the air and spam Perfect Attacks from a safe distance and use Divine Launcher if the boss holds still long enough.
So with my play-style (and from the sound of it yours as well) "laying traps" is a waste of time. Sure, it has a certain purpose in certain, very situational, scenarios. I've never seen any reason for it. Manage your PP well enough and you won't have any need for them anyway.