If one wants to transfer a big amount to a external recipient, it can happen that you need a lot of input-tx to fund the spending. For each input one has to do PoW so ideally your bundle is as small as possible.
I was wondering whether Flash could be of assistance here. The idea is to create a flash-channel with yourself. Then you sweep the funds from multiple addresses to 1 particular address superfast offline (all belonging to the same seed). Result is that 1 address contains at least the necessary amount. This way you can send out a small bundle where you only need 1 input (which saves unnecessary PoW).
Question: i think this sounds too good to be true but would this be possible?
The point you are missing: When you are creating a flash channel, you have to reference all the incoming addresses by one transaction each (once). So you will need do to POW for that number of transactions anyway.
What you can do (of course), with or without flash channel: when you notice that you have too many addresses with balances, just send your whole balance to a new address of your seed. You'd have to do the POW then, but when you later have to pay something quickly, you only need to do POW for one input address.