Tailoring is not just a skill you have to repair armor. Tailoring is essential for a warrior who likes to hunt light. This skill allows you to do two things. First you can tailor body armor to make it lighter and more protective. Second you can use this skill to Create new armor as you reach higher insights. You can -not- use tailoring on any armor that has already been dyed or tailored.
There are four kinds of tailored body armor. Good, being the least impressive; Fine, an average tailor; Grand, a magnificant tailor; and Great, the best kind of tailor there is. Good armor makes your body armor have a -1 bonus to your ac and is 20% lighter than normal. Fine is a -2 bonus and 40% lighter. Grand is a -3 bonus and 60% lighter. Finally, Great is a -4 bonus and 80% lighter. Practice your tailoring every day, with an assistant if you can, on normal clothes that you can buy in the Mileth tailor. The more you practice, the better you get.
Tailoring is also required if you wish to create (which i know you will) better armor past the 11th insight. You will need about 3 days of labor to create the 26th insight and 41st insight armor. Any armor beyond that requires a full 7 days of labor. Without tailoring, you wouldn't even be given the option to create such magnificant pieces of protective clothing.
Here is a table of what you will tailor per legend level
