It's actually not a rule. If you like recapping other people's posts and you can still post at a decent pace then go ahead. The reason it was discussed in a negative manner is because it had a stultifying effect; the recapped posts were taking such a long time to type up that the RP was moving at a lethargic pace. With multiple roleplayers in a scenario, a slow poster will inhibit everyone else involved from being able to carry the plot forward.