I don't like join-up.. It's sending the horse out of the 'herd'. In the wild it would mean he's on his own and that's a dead sentence. It's very stressing for the horse. The horse comes to you because he needs to come back in the herd, it's his only way of surviving!
Of course these are not wild horses, but their instincts are just the same.
I understand it can be useful for problem horses, but then only with someone who knows what he's doing. And not just for 'bonding'.
Like most are saying here, the most important thing is that you're the leader. The horse must have respect for you. Spend a lot of time with your horse, not only riding, do some groundwork for example, or just brushing your horse is bonding too.
When I started with tricktraining we bonded a lot. But it's not just about teaching the tricks. That would be very dangerous teaching a horse to rear for example without any respect and leadership. Respect and leadership, you need it for everything you want to do with your horse.
Sorry for bad english