think about this. you probably have 200 amp service to your house. that's 20,000 watts (approx)
just because you plug in your fridge doesn't mean it's getting 20,000 watts. that's what is available for your use. it only takes what it needs.
do not confuse watts with volts (electromotive force). you can't plug your 110v fridge into 220v without frying it.
just because your power adapter is 65 watts doesn't mean that much electricity is flowing to your macbook when it is asleep. 65 watts is the max available that can be used during battery charging + hdd access + screen display + ram use, etc. etc. when your needs get close to using all the available 65 watts your charger will start getting hot, reducing the charger's life.
at times you may be bumping or exceeding the 65w limit when everything is being used. an 85 watt charger is a great idea. upping your charger is just like upping your ram or hdd etc.