We have a saying around the Club here in Peterborough “ Single Heavy Weapon in a Squad! “ This is for any squad that has that one random Heavy Weapon that never seems to do anything. At least I have never seen them do anything to amazing. Sure 1/50 times you might get that lucky Land Raider pop or take out a Rhino, but in all honesty the points you save from not bringing those over priced Heavy Weapons gets you a lot more scary choices in your list.
This works with almost any Troop choice to be honest. Troops all around are just NOT WORTH BRINGING FULL SQUADS OF! This changes with some armies but about 80% of the armies in 40k this Rule holds true. I would say Nids, Orcs, IG have troops you want full squads of but a lot of other races its just not worth it. 9/10 times the things you replaced those troops with are going to do a lot more damaged on the battlefield.
Lets take Eldar for instance. Its 60 Points for 5 Dire Avengers. You throw them in a Falcon if you are taking Falcons or you get them a Wave Serpent. Maybe even put a Bright Lance on that Wave Serpent so you have some extra Long Range Fire Support. If you got the 10 man squad of Dire Avengers then the squad jumps to 147 ( You have to take bladestorm if you are bringing a 10 man squad ). That's an extra 87 points for something that won't do as much as people think. Now some people like the Bladestorm+Doom Combo, but I myself am not to fond of it. I would rather be doing other things with my Farseers then backing up some Dire avengers.
So we spend an extra 87 Points per squad on our Dire Avengers to get them to 10 man squads. Lets say we are playing 2000 Points and we have 4 squads of them. That's 348 Points that you could have spent on something else. 348 Points is a lot of points.
Think about the person you are playing against. If they spend those 348 Points in Troops, and you are putting those points into scary things such as, Termies, Dreadnoughts, Land Raiders, Carnifexs, Fire Prisms, Warlocks on Bikes, Nobz etc, then there job is that much harder now. Getting rid of troops to bring more use full things helps a lot in the long run.