When repairing splits or cracks in an acoustic guitar which has a solid top, back or sides, the challenge is usually in addressing the damage to the finish. It is impractical to strip off the finish and re-lacquer the whole surface just for the sake on one or two splits. A better course of action would be to touch up the lacquer in the immediate repaired area. However, this also has its problems as lacquer tends to shrink back in time thus leaving a small indentation.
In general, splits that have opened-up due to the drying out of the wood will not close and therefore have to be spliced. This is usually the case in older or dryer instruments. Unfortunately the splice is usually visible.
Quite often a split can be sealed on the outside with hide glue and cleated on the inside to reinforce the damaged area.