In general, using jigs and the like can add precision to your finished work. Some times they make your work go faster, and some times the set up is more work than the finished product needs. I use dovetail jigs to cut them with a router for drawers because it makes the work much faster, and very precise-- good tough durable drawers with tight joints that look good. I certainly know how to cut them by hand, but it's a lot slower.
You will have to decide if you want that level of precision. For lugs all I really care about is if they are reasonably solid and most of all, functional. Since they're held in place by the wood in the channel, if they're a little sloppy that doesn't matter so much. With sights, because they're so critical to the ball hitting where you aim, it's more important that they be tight, and of course, it's nice if they look good too, for aesthetic reasons if no other.