I think it's unreasonable to make a blanket rule of no friends to play, or going over to play. (cant do the word playdate)
Every child is individual, and every term can be different in terms of who's socialising with who.
I have 3 DDs. Teens now. DD1 had 1 good friend all through primary and all through secondary, who came for tea and sleepovers when they were young and who became, and has remained, such a good family friend that she was invited to my (very small) wedding last year :)
DD2 never really had many friends over to play/sleep. She just wasnt into it. Plenty of firm friends through both schools none the less.
DD3 had an awful time with friends in primary. Her year seeme full of prima-donners. Constantly falling out and making up. A scattering of invites out, no one special enough to ask over. Now in secondary she has a firm friend (at last
) who does come over and has slept a couple of times. They have just been away on an activity holiday together, at 15, which was lovely.
All 3 DDs have grown up normal, social girls who have no problems making new friends at college, clubs etc;, despite being quite different socially at school.
I think IF your child has a special enough friend to invite/be invited by then it's nice to nurture that friendship.