When an ally with this feat charges a creature that is no further away from you than your speed, you can, as an immediate action, charge that creature. You must be able to follow all of the normal charge rules.
The normal charge rules say charging takes time... this feat says it's immediate.
A lvl 4 rogue scout gets to sneak attack whenever he charges.
A cavalier is basically built on charging, and can ride through (right on by the enemy) when charging. Also his speed is quite high, so the feat could trigger almost whenever the rogue charges.
So round 1 first cavalier charges and rides through, rogue is still too far away to join. Then rogue charges on his turn, feat triggers, immediately cavalier charges again? Then the rogue spends the next round running away to get a little distance, the cavalier charges, feat triggers rogue gets to join?
What about two cavaliers? That would get really crazy! Doesn't that basically ruin the action economy or am I misunderstanding something here?