Question about SAP Dialog work process and PRIV mode

Hi experts,

I have a question about NetWeaver AS ABAP Diaglog work process, according to SAP documents, that one dialog work process can process one transaction step at once, that means if work process 01 is working with user01, then user02 cannot use this work process. When the work process enters PRIV mode (heap memory allocated), no other user can access this process.

My question is, what's the different between these two scenarios? Either way the work process cannot handle other user request at the given time.

As long as heap memory released, the work process is free again, can anyone please explain me the details?

Thanks,

Michael