In the past, a shaded solar panel could bring down the power output of a string in your array, much like a single dead Christmas light kills the entire string. However, by putting a single, small micro inverter on each solar panel, this deficiency can be avoided because the conversion from DC to AC occurs at each panel, rather than in a single central inverter.
Micro inverters also allow for design flexibility and the ability to grow your system in phases, as you are able to add inverters/panels (up to the string limitations) at your convenience.