My Dad is a tailor, from ye olden days as well and cut his teeth measuring, marking and cutting. Yes, you can get a made to measure suit that's pretty much damn near perfect but when a truly experienced tailor works to produce a suit it's essentially a hand-crafted, one of a kind piece of art.
And oddly given my love of tailored suits I generally buy off the peg ones as I'm way too hard on clothing to justify the outlay (even with a family discount).
Beyond the skill of art, I would imagine that an advantage of a practiced tailor is also that you get to benefit from their knowledge of which styles or cuts would work well for your particular features, intent, and life story. Software can get the geometry right, but it's hard to program taste.
And oddly given my love of tailored suits I generally buy off the peg ones as I'm way too hard on clothing to justify the outlay (even with a family discount).