When the map is relatively small, it takes a few milliseconds to save it, so it's generally ok. But with other, much much bigger maps, it could take several seconds, which is both annoying and hangs the game's networking, and overall leads to many problems.
Threading kind of is the answer, but it creates another problem — while map is being saved, all changes user makes are also being saved, after the save button was pressed (so if the user decides to blow up the map right after pressing Save button, he might be unaware of that it might be saved). So this either calls for user-map interaction block until map saves, or something else entirely.
