I'd much rather save my frag grenade for when that 'perfect moment' does come, than not have it handy when it does.
Nothing wrong with conserving ammo. Ghosting can deplete your ammo alot if you don't have Bandolier, so why not be a bit more careful when taking someone out?
And reloading after killing someone can be very helpful. It could be the difference between life and death (virtually of course), but not many people are stupid enough to do it whilst they have an enemy in their face. Introducing Mr Pistol and Mr Knife...
I guess I should have specified that this is mostly for objective based games. Ghosting is a seperate issue, and I'm not saying don't conserve ammo and blind fire. I'm saying if you fire 4 rounds to kill someone with an m4 when they come in the door, you don't have to reload immediately. There is a good chance someone is just far enough behind them that you have time to trigger the reload before you see them there. Reloading after every kill when camping in a building with an objective will get you killed much more than save your life. Unless you wasted the whole magazine on them, but that is obvious.
I'm not saying don't reload period, but reloading immediately after getting a kill USED to kill me, and I still see it kill quite a few others.