First thing I wanted to discuss was this recent negative stigma against trapping abilities. See, trapping is actually very healthy for our metagame. Shocking, I know, but please allow me to explain the purpose of trapping and why it is healthy.
See, Switching is a vital part of our game. Without switching there wouldn't be much of a skill element in the metagame, and without this mechanic the game would simply break because you wouldn't be able to save things / etc. I shouldn't have to explain why Switching is important. However, what I DO need to explain is that if Switching goes unpoliced, it is actually very bad for the metagame.
Sometimes in stall, there is a point where the best play for both players is to double switch constantly, resulting in an Endless Battle of sorts. This is the direct result of one thing: Switching has no cost or risk in these situations. Neither player can punish the other for switching. Now in stall in SM OU, this can be attributed to two things:
a.) Defog + Magic Bounce together is easily able to keep Entry Hazards off the field, rendering them practically unavailable for most of the match.
b.) No Arena Trap / Shadow Tag / Pursuit user (keep in mind that in the Pursuit user's case, it oftentimes isn't strong enough to really stallbreak
In this example, if these stall teams had Dugtrio it would actually have been a healthy presence as Dugtrio can stallbreak and force each stall player to play skillfully around it.
However, this isn't the point I am trying to make right now. The point is this: trapping is part of many switch-punishing mechanics in Pokémon, the others being:
a.) Entry Hazards
b.) Trapping-Moves (Pursuit, Anchor Shot, Spirit Shackle, etc.)
c.) Trapping Abilities (Arena Trap, Shadow Tag, Magnet Pull)
Other things help switches (U-Turn, Volt-Switch) and all of these things keep Switching balanced and keep it from causing Endless Battles or being overpowered in general. Punishing switches is a good thing, and this is why trapping is a healthy force in our metagame.
It's not just healthy because it stops Endless Battles from occurring, but it is healthy in general to punish your opponent from switching, and trapping as a mechanic is a good one. (Some trapping ability users like Gothitelle are broken, but others like Magnezone and Diglett are not.)