Theres a number of reasons to go traps/mines/totems.
all avoid reflect. the trap/mine/totem casts the spell. At the same time, no leech however either.
They bypass cast times. Arc with a .8s cast time.
Mines and traps have .5s laying speed default.
Remote mine is 40% more damage. Minefield is +2 mines, 21% less damage.
so, its a 40% more damage support, and in the case of spells with large cast times, a hefty cast time increase. Then with clustertrap/minefield another huge cast time buff, by casting multiple times at once.
minefield with 21% less damage, and +2 mines, is 137% more damage.
trap/mine, minefield/cluster trap are pretty large dps gains directly.
Mines come at the price of needing detonate remote mine DROP only skillgem, linked to spell totem. a 2 link, and pita for SSF.
Traps come at the price of delay on activation, and need to be activated by NPCs themselves. As well as cooldowns. This is what is being addressed in 3.0 NO cooldown on certain trap skills, including trap support. AND, traps auto activating on Duration timeout. so, still a delay, but they WILL cast now, and never be wasted.
Then obviously, more specialized things. Inquis/scion passives for totems. Sab traps/mines, etc.
old arc.
47-886 damage. 466.5 ave. x1.25c/s. 583dps.
+remotemine. 653ave x2c/s. 1306dps (1 link, +totem detonate mine.)
515.9ave x3 1547.6 x2c/s. 3095dps cluster mine 3mines/cast. (2 link, +totem detonate mine.)
new arc.
152-862 507ave. x1.25c/s 633.75dps. x105% more damage. 1299 dps.
887 ave x 2c/s 1774 dps remote mine. x105% more 3636.7
700.7 x3 2102 x 2c/s. 4204 dps cluster mine. x105% more 8618dps
Arc especially works well wit cluster traps/mines. Since it auto targets, and gets dramatically increased single target, and coverage with it. without, arc gets its 8 hits in, and stops. compared to a gmp peircing attack, which will hit 50 /50 of beyond mobs. While a minefield arc, will hit 24/50 vs self casts 8.
Mirror arrow and arc, auto activating on timeout is huge. Projectile skills can miss when activating far from target, AOE skills also miss often. arc never misses. 5/5 cluster traps will hit on target.