Again, it’s just another option you can work with. Sometimes it fits, sometimes it doesn’t. For VPN clients as “fake in-LAN devices” it’s just a half-solution, but good enough for some. If you want full L2 (@rextended’s example), then proxy ARP is not a solution at all. But it can be pretty good solution, given the circumstances, if you’re getting multiple addresses from ISP, but instead of routing them to you separately, they’re part of ISP’s subnet, but you need to route some further and L3 is all you need. Then you can use proxy ARP to make the address visible to ISP’s router, as if it’s connected locally, but you can route it to other end of the world if you need to.
IT boyscouts and their swiss army knives… I just have a can opener. 
ROFL 