I think the "ok" thing is ok and healthy if it is agreed upon between both parties and the reasons are understood. For us it was better than me getting angry all the time. And as time has passed I have needed it less and less but it is always there. If my friend is confused by my asking we talk about why although usually it is obvious because my friend was extra busy or traveling or whatever. I don't know; it works for us. I haven't introduced it to other relationships though and I don't know if I ever would.