It does help, as the new growth has better access to full light without being shaded by the old dead leaves. In nature this happens with grass fires burning off the old dead growth every few years; this method isn't always safe in gardens of course! When cutting out old leaves, wear heavy-duty hand and arm protection to avoid getting cut by the razor-sharp leaf edges.
Try pulling the oldest stuff first. It usually comes out easily if an old clump. As Michael said make sure you are well gloved and arms etc protected. I would also wear something over the eyes. If you do decide on fire make sure you are no where near a building or fence and have a hose handy. They go up like rockets but the job is done in minutes and the regrowth is really nice. I used to fire mine once every 3 or 4 years untill I discoverd they are a noxious weed here. Liz
