4th edition D&D--new combat mechanic

[ororo]

I'm not sure where our DM got this information, but we started playing with a new combat mechanic. Basically, monsters have half their hit points BUT deal max damage. This has the advantage of speeding up combat considerably, yet making it a little more challenging.

Has anyone else tried it? I'm wondering if there's a downside I haven't seen yet, since we've only used this for two sessions.