For most people, yes. But this question is not quite that cut-and-dried.
Most people do not actually use an operating system. They use applications. The applications are what really use the operating system. FreeBSD is designed to provide a robust and full-featured environment for applications. It supports a wide variety of web browsers, office suites, email readers, graphics programs, programming environments, network servers, and just about everything else you might want. Most of these applications can be managed through the Ports Collection.
If you need to use an application that is only available on one operating system, you simply cannot replace that operating system. Chances are there is a very similar application on FreeBSD, however. If you want a solid office or Internet server, a reliable workstation, or just the ability to do your job without interruptions, FreeBSD will almost certainly do everything you need. Many computer users across the world, including both novices and experienced UNIX administrators, use FreeBSD as their only desktop operating system.
If you are migrating to FreeBSD from some other UNIX environment, you already know most of what you need to. If your background is in graphic-driven operating systems such as Windows and older versions of Mac OS, expect to invest additional time learning the UNIX way of doing things. This FAQ and the FreeBSD Handbook are excellent places to start.