With NCO you can target frequencies with spectacular accuracy as opposed to PWM or other methods. Many of the newer PICs with NCO also have the option of using LFINTOSC and MFINTOSC with NCO for a slower-than-Fosc(/4) clock. My current project targets frequencies as slow as 2 Hz, with accuracy to 0.02 Hz, and as high as 3.1 MHz. NCO lets me get that accurate.