Hermes posted a video a while back on climb technique, in that the pro said to let the bike swing a little under you. I have tried it both ways, keeping the bike steady and letting it swing. Here is what works for me, swinging the bike is better in all cases except for one - and that is when I am winding up high cadence while OTS - then it is better to steady the bike out. In a normal OTS climb some swing actually is more relaxed for me but when the bike spins up it effects stability.
AJ had a lot of good advice in his post - read it carefully. Also - Stapfam and Bean had some sage advice, if you are a stronger seated climber you will kill them on the hills.
I use the OTS position for these few things,
1) Charging a short hill - you know where the top is and you just want to stay on top of your gear and keep you momentum up and you would need too much spin to do it seated.
2) Getting back on top of your desired gear after you have begun to lug.
3) I need to use different muscles and or stretch.
4) On training rides where I will go up a hill in a big gear intentionally - kind of like one legged leg extensions on a weight machine.
My biggest problem with OTS while sprinting a hill is keeping the bike on the ground, this involves balancing the up stroke and the down stroke of the two feet, sometimes I will start to bunny hop the bike up the hill and that is just not efficient - it usually means I am putting too much up stroke and too much pull on the bars.