OK, I'll have a stab at it, Zamber.
As usual, it depends! First thing, until sails are near end of useful life, repairs
are not often required. The first thing to go usually is stitching, often in way of the shrouds or other chafe inducing bits... and stitching is easy to renew yourself. By hand is often easy enough, but if there is a long bit of parted seam, then a machine will surely help speed one on your way. IMO there is no need whatsoever to pass that on to a sailmaker
Beyond stitching, small tears, often from snagging the sail on something sharp like a cotter pin can also be hand stitched and then reinforced with a small patch made from cloth of similar nature to that of the sail. I've done a few of those on white sails, and a few more on kites, for they are more prone to such damage. Again, no need for the pros here.
But as the sail ages, its strength wanes and larger tears are possible, perhaps to the point of needing a new panel, and that's a bit much for a simple sailor to handle. This is both from the point of handling a big mass of cloth, lots of stitching and reinforcing, and also from the need to shape the seams correctly to maintain sail shape. For such repairs
a pro will likely do a far better job than you can. If you are in the woop-woop and no sailmaker
is in sight, and you have the needed cloth and a space to work
, well, a poorly mended sail is better than no sail at all, so give it a go.
As to local or send out, I'm always in favor of using a local sailmaker. You can take the sail to him and spread it out and discuss the options for repair. Most any sailmaker has the skill needed to do even big repairs, so don't worry much about the ability of a local. In fact, he's more likely to do a good job if he has had a chance to chat with you personally.
So, there's this sailors thoughts on your query.