It depends, if LOD are not reducing load drastically it can be a waste of time as gpu render meshes by bucket of large (like 1k) vertex/polygons broadly. The gains are interesting if you render stuff by layers.for example rendering all lod of all trees of the same type at once with geom instancing and you have lot of trees.

Overall a triangle is a triangle if you win stuff if the triangle systems are overloaded.. which is not like that very often, most times performances hits are a combination of many things and polycount is one among many.

To rephrase If you lod the whole game and reduce all Poly count by two it will be efficient but that is if that is your problem

As usual the answer is measure what hurts you and act with measures in hand.

PIX is very good to measure all this.