i couldn't understand the comment that "the application running in user space cannot request more memory" - can someone explain whats the point of memorybalooning anywhere if an application cannot signal when the system should actually provision physical memory from the 'baloon'

There isn't a point, that's the problem.

The systems administrator can use ballooning to give more memory to a VM before launching a new application. This avoids the need to shut down the VM to give it a new role.

There is still a benefit to ballooning support even if it's not exposed to userspace within the VM, because VMs aren't always used purely to host a single infinitely-long-lived application without outside intervention.