A lot of our time we work with log footage and use an adjustment layer on top layer with the Apply Color LUT effect. This slows down the whole comp more than I would expect a LUT to do as this should not be a heavy effect (see Premiere's realtime implementation for a start). Secondly it usually means slower final renders as the cache contains renders with the LUT on but we obviously want to output as log. A more elegant solution would be to be able to load a LUT into the composition viewer and let the GPU do the colour transform.