Advantages

Designers use FPGAs for  a variety of reasons.  FPGAs are, in many cases, a very compact and cost effective way of making special purpose electronic circuits.

A major feature of FPGAs is that they are programmed by the company that buys them (ie. they are "field programmable"). This means that the company that makes the FPGAs (the silicon chip foundry) does not need to know what circuit function the engineers need before they are made. In this way, FPGAs can be mass produced as "general purpose components" and bought "off-the-shelf". Cost saving and faster time to market for products are often the results.