The nice thing about S-Boats, as some have already said, is the increased challenge
I am currently playing a campaign with an S-Boat (Asiatic Fleet) without using the TDC, using only the SACF MKIII to shoot my torpedoes and this is a BLAST! I will write a short tutorial for that soon, for anyone interested in shooting torpedos without TDC in these Pigboats

(Note that it will require that you have a wiz-wheel, preferably the SUbmarine Attack Course Finder, or a slide ruler)