When I started playing, I played Ultramarines. Being 12 I had no idea what I was doing so I just built the squads with what they had. The old tactical squads in those days only had flamers and missile launchers, so that's what they got.
Then I moved on to space wolves. Their upgrade spree came with a melta gun and power fist and power sword and an axe, so naturally my squads found themselves armed to the hilt with as many legal upgrades as I could fit into a unit. A couple of additions ago, I figured out that this made my standard Grey Hunter squad cost over 200pts and that this was a stupid way to go about it.
These days I have a purpose in mind for each squad. I'll tend to kit a squad with melta x2 and a combi-melta and ditto with the plasma squad. The beauty with these units is that plas can take out light vehicles and rear-armour almost as well as melta will and melta is pretty handy at taking out heavily armoured troops if there aren't any vehicles nearby. Then there's usually an assault unit in there with a couple of power weapons and CCW.
I think, Mr Mystery, you e just grown up and become a sharper player, cutting out wasted points and maximising the utility of your units. As Yorkie points out, a squad that's equipped for close range anti infantry and long range anti tank isn't any good at either and is ultimately a liability.