I don't see a lot of usefulness in a substitute set. I guess it does come in handy sometimes, but only for Focus Punch and stall sets really. Substitute is useless for the most part if you're just using it to be using it. It's very good on subseed sets, though. I'm sure you're familiar with Whimsicott, which is an extremely good subseeder. I've seeded and poisoned various enemies and then subbed up to take the damage from more painful attacks easily thanks to substitute. Aside from that and Focus Punch, there isn't a ton of usefulness behind it.
The viability behind setting up behind a substitute doesn't make sense to me. If you're making a sub, you need a guarantee it won't be broken as soon as you make it. If you're setting up on a Pokemon on a switch, a Substitute is useless, as you could have set up the sub just as easily as you could have swords danced on the switch. Thinking about it, though, you could easily resist status ailments with a sweeper if you set up a sub on someone. It's not a bad route to go if you have an extra move slot.