I came across a Focus load program that loads a multi segment mainframe Focus DB. At the end of the load there is "table file" that counts all the segments in the new db. When I suggested to remove it, I was told that since this file has aditional "referrence" files it is necessry in "exclusive mode" to parse all the segments in order to populate adresses or pointers of the referrence dbs. If this is not perfromed the performance will be significantly slower. Is it true? If yes it is still valid today? Can someone explain this to me? This query is very cpu costly.

If the masterfile of the database contains references to segments outside of the database itself and if those references are static, then this method of tabling the file after creation or loading is indeed still valid.
A static join in the master file (segments with segtypes of Kx) will reserve a pointer in the database that will only be resolved using table.
If you do not resolve this pointer then this will be done when the record is referenced for the first time. So only the first usage will pay the performance price, after that the pointer will be used and it will be updated only if needed.
Depending on the size of the databases this can indeed be quite costly.

Hope this helps ...