This is a big area of discussion and difficult to summarise. There are pro's and con's for configuring frame-relay on p2p, p2m and on the physical interface. It really depends on your design requirements. P2P as the name suggests just has 2 devices connected while P2M can be hub and spoke or full/partial mesh. routing protocols work in different ways depending on how the frame-relay is configured (see ospf network types and eigrp/rip split horizon). The choice of frame-relay interface also has implication on how multicast will work.
So to summarise, if you have many frame PVC's in a hub and spoke topology and use P2P you will end up with lots of subinterface which may be undesirable. P2M can get around this issue as the spoke will only need one interface, but there are other issues to think about if you use P2M.
