Size - that's about it. Good for installing in smaller build PC's, but no less powerfull than full size boards. Drawback is you will have less slots available for expansion of additional...
Size is the advantage.MicroATX is usually much smaller than normal ATX and usually has fewer expansion slots like PCI (+variants), fewer DIMM sockets (usually 1 maybe 2) they are often built around...
ATX improves upon AT by making adding and removing components easier, providing greater support for I/O devices and processor technology, and lowering cost.