The best one is async routing. You have a NAT, they have a NAT, you VPN together and think you have different IP address ranges, but unknown to the operator there's a little internal network with an overlap at the end of some slow line that is now getting flooded with internal traffic that's trying to go to a completely different network.

I've worked for companies with over 50,000 employees and they didn't seem to need it. Now, sure, there are larger companies, or ones that employ huge farms of machines, but those are the exception rather than the rule.