Requiring a shield to be active as well, Block Runner mostly helps you close ground when you Shield Charge or just generally have to deal with archers and mages. The rest of the time, it’s not going to mean too much, since melee enemies who are fleeing aren’t attacking you anymore anyways. This doesn’t make it useless, but it does keep it from being a terribly strong perk.
This perk’s benefit is invaluable if you like to hide behind a block, even if that block is a bow. Particularly useful for knocking an enemy’s weapon clean out of their hands when they try to power attack through your block, and even if your enemy has a backup weapon, it’s probably not as strong as the one they were using- so this can really turn around a fight. Sadly, the Disarm Shout does pretty much the same thing in a much safer and perk-cost-free manner before you even need to block in the first place, so if you can find out how to get that shout you may find that this perk abruptly becomes useless, or at the least drastically less useful.
Requiring a shield to do anything, Shield Charge gives you a way out of corners and surrounding circles of enemies, as well as making a decent tool for shoving people off of cliffs and fortifications. Combined with Block Runner, it can go a long way towards getting you some breathing room mid-battle to refocus yourself or changing your position to get the advantage in combat. Or you could just topple people for fun, if you’re so inclined. If you never need either of these things, though, you won’t find yourself using the perk at all.