Concurrent request submitted by other concurrent request

Is it a good or bad practice to have PL/SQL code being executed by one concurrent request submit another request and than wait for that request to finish.  This will take two available slots for request to run in.  If I get a bunch of there all running at the same time taking up all available slots can I hang the concurrent request manager.  All the request running will be waiting for other request to finish and those request can't run because there are no open slots.