Well, one other drawback to using something like BoincTasks is you have to be able to contact each machine. So if your hosts are behind firewalls, say your workstation at work, one at home and one at "Moms" house, it becomes a bit more difficult to remote control them. Similar problem if you're running VM's on your hosts using native NATing. The VM BOINC has the same "address" as the Host instance of BOINC, so you can't control both from something like BoincTasks without getting freaky with alternate ports and such.

Using a Manager like BAM, once you've set the hosts up, each host initiates the check to see if there are any changes. So, if it can "call out" to Projects to send/receive WU's, it can contact BAM to be controlled. Even if it's multiple VM machines running on a single Host.