I actually just read an article that said its best to prune maples in the summer so they don't ooze sap. In general, maples only need pruning if they have crossed branches, damage, or if they need to be limbed up because of low branches. Never remove more than 10-15% of the branches in any one growing season, as this can affect growth and will result in lots of suckers and water sprouts forming.

Regards,
K4