Ozgun,
You can have two holds for one waypoint. For instance you might have a hold prior to an ILS approach and a different hold, at the same waypoint, for a missed approach. Try putting any more into the FMC and you'll find the latest one will go to the top of the LEGS page and 'overwrite' the existing one. Obviously the missed approach hold is at the end of the legs. Why would you want any more?