Straps forward in general loosens the tail of the board up, as the rocker is elevated, weight is further forward so more rail is used in the turns too. You have more control too, as the nose is not riding too high Straps back means you will turn off the back foot (front foot for straps forward), good for lots of short, sharp turns, especially in onshore conditions. lifts the board out of the water, making it very lively, but also harder to hold down.
Wave sailors mostly further forward than racers or freeriders. Freestyle somewhere between, but now with sailing backwards and spinning tricks, the Freestyle straps also are going quite far forward, to be “centered” in the board for balance! Racers mostly furthest back for most speed and lift, also much further out on the rail.