There are pros and cons to both types of recording.
Here are some reasons why I prefer to record on a BR:
1) Portability. I can take the BR to wherever my guitars and other musical equipment are located. If I recorded to a PC instead, I'd have to take my instruments upstairs to my cramped home office where my desktop computer is located. I could manage to take my guitar upstairs to record but I'd have a hell of a time with the piano and drum kit.
Of course, if you have a laptop you can take it to where your instruments are. But there are always cables to disconnect before you can move it, so it's still a pain.
2) Noise. Computers make lots of noise. Fans, disk drives, etc. are constantly whirring away making lots of noise which you don't want to have picked up by your microphones. Of course, some computers are noisier than others but even the best make some
noise. But the BR is completely silent because there are no moving parts. This is one reason why I prefer recorders like the BRs which use memory cards for storage instead of hard drives.
3) Updates and technical issues. With computers, you're constantly updating drivers, programs, O/S, and hardware. And you have to constantly wrestle with technical problems such as latency and incompatibilities with programs and drivers. With a BR, you just turn it on and it works. So you can concentrate on your music instead of your computer.
4) User interface. Computers have the advantage of a nice big display. However, they lack the tactile control of the BR. Track levels on the computer are adjusted by dragging the mouse on a virtual fader graphic. This can be difficult to do smoothly and accurately. With a BR such as the BR-600 or BR-900CD, you have real fader controls which are much easier to use and give you smoother, more accurate control over your levels (unfortunately, the Micro BR does not have real fader controls; it uses two +/- buttons to control levels). Of course, if you have lots of money, you could always buy a hardware control surface for your computer which would give you real faders, transport controls, etc. But the cost of a control surface can be more than the cost of a BR. Oh, and you'll probably need to buy an audio interface and some mic preamps for your computer too.
5) Convenience. The BR is an all-in-one recording solution. It includes lots of great effects, a built-in drum machine, and built-in microphone (two in the BR-600). Just plug in your guitar and you're ready to record. It's the simplest, most convenient way to make multitrack recordings.
6) Cost. If cost is an issue, get a Micro BR. It will be much cheaper than buying DAW software, and audio interface, microphones and preamps, etc. If you can afford to spend a bit more, get a BR-600. It's almost as portable as the Micro BR but offers a LOT more features, including the new Drum Editor software (free download).http://www.roland.com/products/en/BR-900CD_Version_2/images/info_03R_L.jpg
.. oops! I just realized that you already have a Tascam interface, mics and software. In that case, you might as well experiment with it and see what you think. Afterall, it will cost you nothing to try it. But consider my comments above. You might want to try a BR after you've experienced some of the computer issues I've mentioned.