MIB overlapping also enables you to delegate all unhandled OIDs to a legacy master agent, such as the Solaris agent snmpdx. If you register an SnmpProxy at the root of the OID tree, then all varbinds for whose OIDs no SnmpMibAgent was registered are passed to that SnmpProxy.
In addition, MIB overlapping enables you to give precedence to a specific agent for a part of a MIB, by registering it deeper in the OID tree.
For a get-next or get-bulk request, the incoming OID does not make it possible to identify directly the subagent that will contain the next OID. Indeed, the next OID might not be a sub-OID of the requested OID, but might be in a different part of the global OID tree. The get-next and get-bulk requests are thus forwarded to all subagents, and sorted a posteriori to identify the deepest matching subagent.