In theory it's a good thing and one can demonstrate that the performance
increases significant with larger queues. But if the hostadapter for
some reason decides to execute first all commands for one target, then for
another the timing for feeding the CD writer with more data might become
very problematic.
Another problem is that the SCSI command queues often a being filled up
with commands from just one device. This results in making the SCSI bus
temporarily unavailable to other targets and can be pretty annoying with
tapes.
Ralf