They can make Bio-enhanced clothing (using tissues acquired from a Bio-Engineer) which can increase certain skills. They also make some components used by other crafters. Tailors do not perform experimentation (except for Wookiee Armor Segments), so resource quality is not a factor for them - any old stuff can be used. Tailoring IS a labor intensive profession, though - since each piece of clothing can have different colors, most clothing is made by hand, rather than in factories.
This profession requires 92 skill points to master, 29 of which go towards prerequisites