I use them in Drop Pods. Full ten man squads. I run Salamanders, so it's flamer, multimelta, and then melee weapon (I vacillate on which) and combi-melta on the sarge. The ability to switch up into combat squads lets you field an
MSU list if that's going to be beneficial to you. (And it almost always is.)
Two squads out of a pod can do a lot for one another. One squad can peel back bubble wrap so the other can pop a transport. Alternately, one squad can bust a transport while the other squad annihilates the former occupants when they get out.
Tac squads are pretty cheap, and while they aren't first string picks in ANY battlefield role, they are solid second and third stringers in almost all others. What they excel at is picking up the slack if you have an unexpected setback elsewhere. They can't carry a game on their own, but they can absolutely help your other units, your dedicated-role units, carry their own weight if something goes wrong.
There was a bit of a debate when the codex came out about the best troop option. While bikes are still a solid choice, I've grown accustomed to Deep Strike tactics, and bikes can't do that. Tactical squads are a solid pick too, now. Of course, with 7th edition's removal of area terrain and the fact that sniper rifles are categorically worse against vehicles (functionally useless, I'd venture so far as to say), scouts are back to riding the pine as second-tier troops choices.
If you have any specific questions about tactical squads and loadouts, feel free to
PM me!