Toys teach your child the needed skills for a healthy development but it also introduces them to social skills and friendship. Sharing toys will allow them to make friends who are interested in the same toys as them. If they rent a toy, knowing in advance that a few weeks later they will have to return it, they will start talking about it to other children around them. This works for books and visual content too and it allows your child to have common things to talk about with children their age.
Also, sharing toys will teach your child to be responsible when it comes to playing. Knowing that this is a shared toy, your child will do their best to take care of it which will improve their planning skills, their control over their movement and their behavior.
Sharing toys will also allow the child to develop their understanding of negotiation and also to cope with disappointment when things do not go exactly the way they wanted.
Renting a toy and returning it while having the option of renting another, will give your child the exact feeling they get in a library, the feeling of knowing that endless options are at the reach of their hand. This broadens their scope of interest and makes them even more curious about exploring new toys and thus new skills and imaginary worlds.