What I like most about it is simply the fact that you can control every parameter on you old synth from the ease of a well put together (slightly confusing at first) GUI on your computer. Saving these presets (or sysex dumps) is also awesome. This way I have no limit of sounds I can create on my old synths. For the price of a nice virtual syn...
I've been using MOTU FreeStyle for about seven or eight years since I got acquainted with it during school. It is a really easy piece of software to use and because of this it isn't capable of all that much beyond its basic function. This software is designed for beginners and if you are a professional I would recommend looking into MOTU Digit...