Primarily, trading size at the opening in big arb deals.
For instance I bought 25000 ONE Friday and sold short 34000 JPM.
I unwould it for maybe 10-15 cts profit. It wasn't clear it was a "do" at the opening, but I had some little hints I won't share that gave me some confidence to do size. This works best on a triple witching because the opening print is usually large enough to handle the size.
This isn't available every day. And now that I have no bullets I can only do it if one of the stocks is going to be up.
I remember when PFE bought Pharmacia, I did 40,000 Pharmacia on the opening one day and made $1 by selling the ratio in PFE. But, I had to use bullets to sell the PFE. I wouldn't be able to do that today.
I also start trading at 4am PST. I once bought 4,000 Pharmacia (see I can't even remember the symbol) $4 below the market on Instinet. There was 14,000 offered. Of course I then immediately started wondering what was wrong with the deal. The stock opened up and nobody challeged the trade.