A possibly stupid Engineer question...
EDIT: This is for PvE Scenarios.
Use your weapon for the occasional crowd control abilities. If you run P/P take a moment to blow off the blowtorch for some additional condition damage. Otherwise as long as your enemy isn’t moving all over the place, use grenades.
Nice thing to do is to switch to rifle, fire net-shot, immobilize your target and use your grenade toolbelt skill to ensure that all the grenades hit the target.
Yeah, mainly use grenades. Your weapon doesn’t outpower the grenadier trait unless specc’ed for power+crit + elixir U + elixir B, and it has to be a rifle and even then it’s single-target and not AoE.
As I said, switch to weapon whenever you want to blast off some additional CC or Condition Damage, otherwise stick to grenades.
That’s how I do it though, and my word is not law, so do as you please.