I've used it to catch Jan Shatabdi and MAS-SRC on a few occasions, but it does cost quite a bit as mail usually ends up going into waitlist before the direct trains from SBC do and we have to resort to Tatkal. :)
Kaveri or YPR-MAS/MYS-MAS/SSPN-MAS are usually better (in ticket availability) if connecting to Howrah bound trains.