This has been discussed here many times, and if you search the archieves
you'll find plenty of material. Anyway, a short summary:

Pro:
- it is safe *if* done properly. Be sure to get thorough instruction by
experienced people.
- cheaper than aerotow
- "greener" than aerotow
- it is fun!

Con:
- it mixes poorly with power traffic (but it is doable if you have a
plan and everybody cooperates)
- boring for the winch driver
- needs more ground staff
- limited in height and distance, i.e. you can't tow to that thermal 10
miles away if there's none nearby