Halo 4 removed the weapon loop - the acquire -> use -> resupply chain that was a defining feature of Halo 1, 2, 3, and Reach.
The acquire phase is your team getting and securing a power weapon (or any weapon really, but power weapons are the best demonstration of it). The power weapon should be placed in the worst place to use it when possible.
The use phase is taking the weapon from the worst spot to the best spot to use it.
The resupply phase is having to go back to the weapon's spawn to resupply the ammo. You can also choose to trade the weapon away for another one, which means you're giving the other team a chance to acquire it.
The key point is the resupply phase makes your team work as a team and cover for you while you re-supply. This also adds a natural "breather" for the other team (ie if they're getting sniped) to regroup and push back.
It also just promotes map movement in general.
What happened in Halo 4 is this critical loop disappeared. You could acquire a weapon in the best place to use it, and then you were rewarded with better weapons as you kept killing, without ever having to leave cover or the good spot. Map movement died. It was pointless to try and control the map because weapons could be spawned anywhere. It felt like when Forging a map in Halo 4, your map design no longer mattered. It was just a backdrop to how 343 wanted you to play, not how the map designer wanted you to play.