Well in the case of that map I know that the lag is a result of the way valve changed some particular entities in a previous update. Removing those entities fixes the map and removes the lag.
As for other maps I will have the ability to permanently add any entity or object to any location on the map. This would enable the creation of good cading spots where they were not possible in the past. Likewise, I can remove objects that make more places impossible or that break maps.