It is one way to have more power than a typical tube amp, and still have tubes in the signal path for more bloom, etc.
Conrad Johnson had their 200 watt EV2000.
Blue Circle has a couple new hybrid amps on the market; the BC24 (80 watts) and BC28 (120 watts). BC's old hybrid amp was the BC6, which was 25 watts and does not fit my power scenario above.