I agree @NuffSaidSam
I can think of a friend of my ds's when they were about 14, who used to come over and have tea with us after school about once a week, for a year. Never crossed my mind to stop him coming just because my ds was never invited to his. It was about 2 years later we found out just how difficult his home life had been at that point and about 10 years afterwards when he said to ds how much he appreciated just "being part of our family" for that one evening a week for those months.
OTOH, I remember that my dd was invited round to one of her friends' for tea after school, and even for sleepovers at weekends over a couple of years when they would have been about 7 - 9ish. I did bring it up with her Dad (which is who I mostly saw), that I just couldn't reciprocate, and he said that it was far easier for him to have his dd and a friend there together, than for him to have his dd there alone, and he really appreciated dd1 being such a lovely guest.
Over the years, it balances out. Sometimes you can help some person in one way, sometimes a completely different person helps you out when you need it.
However I don't see a friend coming round as 'helping out', generally. As a pp said, it is often more complicated to have one of your dc elsewhere, than it is to keep them in their usual routine.