In the middle of combat, I tend to use Spread as either another shuffle or to save a card for later if we're in the middle of a mechanic that won't let me use the currently drawn card effectively. The latter is pretty obvious in its use. For the former, what I mean is if my current RR isn't very compatible with the drawn card and Redraw gives me something equally as incompatible, I'll Spread the new card and hope for a better card next Draw while thinking how I want to setup my Spread card for the future. It doesn't always work out like that but I've had more success than failures with this thought process.

Of course, with anything AST related, you do need some knowledge of the class/jobs you're playing with and the fights you're about to be part of, as well as an idea of how skilled your party members are. Your choices will vary from fight to fight / dungeon to dungeon / raid to raid.