OpenVPN supports more hooks than just 'up' and 'down'. Especially reacting to 'route-up' and 'route-pre-down' events could be important. When routing table changes, it can make sense to adapt firewall, run some tests or change even more routes. This change passes those events to hotplug, so it is easy to react to them without changing configuration files provided by VPN provider.
This has been sent to upstream, in the meantime, let's have it in house.