Tiles take double as long to place, but sometimes they can be worth it. A tile is part of a background that you have saved. You place the tile over an invisible object. This lets you pick between placing a snowy looking tile or a grassy looking tile over the same ground object without having to change the objects code. Making multiple copies of a object so your object can look different gets messy fast, and making your object use different sprites requires you to add code to tell it when to use which sprite so the only safe way to change an objects look is with tiles.