There are many reasons to recommend a bespoke suit. There are the fittings, where you are made to feel like the most important person in the world, there’s the fact that you have something which was crafted for you and only you, and no one else has anything like it, and there is the decadence of owning something so fine, that it looks better the more you wear it.
Your suit is to be cut to fit you, not to disguise you – you will never be that taller, shorter, fatter or thinner version of yourself, so you should look for a tailor who can flatter your body.
A made-to-measure suit is just a basic, pre-existing template pattern that has been roughly altered to fit you, and isn’t bespoke at all. And an off-the-rack suit is, well… off the rack and the furthest thing from being made to fit you. Even with an experienced tailor there are limitations as to how much they can alter an off-the rack suit to fit it to you.