The choice between shared server and dedicated server depends on the type of usage. Typically, if you are expecting 50+ concurrent users you may save memory by using shared server as you are not allocated server processes for each connection. Remember, by using shared server you are placing requests on queues for a limited number of dispatchers to process.
If you don't define enough dispatchers your system will be slower than in dedicated server mode. If you define enough it may actually be faster as the time it takes to make a new connection may be reduced.