@Adel Ouazani1. The NiFi Input and Output ports allow Data to be received or pulled from a process group by the parent process group only. When input or output ports are added to the root process group (top level), there is not parent process group and they assume the role of Remote Input and Output ports used by S2S. There is no may in NiFi to change the functionality. There was an Apache Jira created asking that the functionality of Input/output ports be separated between local and remote so remote input/output ports could be nested in sub-process groups: https://issues.apache.org/jira/browse/NIFI-2933
2. I am not sure what you mean by "a lot of resources", but it is true that a Remote Process Group (RPG) once added to the canvas will continue to communicate with the target NiFi instance or cluster to retrieve S2S details. In order to validate the connection(s), the RPG must always check that the target ports still exist and are in a valid state (running), it must know how many nodes currently exist on target cluster and their current load, etc...
Thanks,
Matt