Well its better to use aged water then water straight from the faucet. When you use a dechlorinator like prime on tap water, it only decreases the ammonia for 24 hours. With aged water, say 12 hours or more, the ammonia becomes a gas and leaves the water, so its much safer for the fish.
Temp wise I'd just adjust it with the faucet, seems easier.
I think your getting ammonia confused with chlorine. Aging water lets some of the chlorine in tap water gas out but it still leaves behind chloramines which is why it is always recommended that you use a water conditioner.
As for temperature.. I don't age my water because if I did my water would be freezing seeing as how I keep my apartment at about 68*F. I adjust my tap until the water is about the same temperature as my tank water and just pour it straight in the tank.
One day when I have the space I'll age my water in a heated trash bin or barrel but I don't have that luxury right now.
Yes I meant Chlorine xD Forgive me, I guess the combination of 4 hours of sleep, water changes and schoolwork takes a toll. And yeah I wish I could age most of my water too, though I doubt my dad would be very happy about extra things plugged in my room >.>
I have a few critter carriers that I use to age the water I usually set it up either a day or a few days before I also have a preset heater that I put in the water so it heats it up I know its not the same temp as the water in the tank but its not cold when I do the change
I think it comes down to personal choice and on the situation! :D
I personally age my water, 1. it makes things so much more convenient for me, it's one less step I have to do when it comes time to do partial or full water changes, 2. my house stays pretty warm, I live in the desert after all >.< , 3. I let the water sit in the tanks with the heater for a couple minutes before returning the fishies to their homes