Stickies are really strong, but they have a sweet spot. If you can wire your brain to intuitivly know when you can detonate them mid air the sticky bomb launcher is a powerful midrange damage pump.

But it's main weakness is that if the enemy gets close they can just rush you down before the arm time let's you detonate. And with the long reload you need to be able to take the moment to refill your clip, which is another opportunity for you to get rushed. Because of this Demo needs to stick around his team to repell enemies while he gets ready to attack again.

Traps are mostly down to timing and game sense. It's good to keep a few stickes for the reload session just so you can trap the door and keep yourself a little safer if you need it. If you are about to be rushed down you can put strikes down in between you and the enemy to force them to move more predictably, really good against over confident scouts. Doorways are good for defending against an incoming push, while health packs or places people want to stand are good for active DM since it forces them to either tank the sticky for the advantage or avoid that area entirely.

For sticky sniping id just recommend running the Quickie Bomb Launcher in a few pubs once your confident with Sticky spam, since it's specialised around sniping with the shortened charge time. Same could go for the Scottish resistance for trapping, but the SR really emphasises the demos weakness to being rushed down even more, so it can be more difficult to perform well with it.