In some cases, yes. But in our testing of planing and semi-planing cats and monohulls, we've reached the point where we always include trim tabs (or if not tabs..interceptors). For all of the more slender of those hulls, particularly catamarans, the inclusion of trim tabs results in a remarkable improvement in the overall L/D of the hull; a 'freebie' considering how small the tabs are in relation to the waterplane area.
And by 'remarkable' I am talking inprovements in L/D ratio on the order of 4-6% typically and that only at a narrow range of speed for a given hull. But still...that's a lot of gain for little effort.
We've improved the speed (and/or reduced the minimum planing speed) on a number of projects through the addition of properly sized trim tabs: A 72' high-speed catamaran yacht, a 45m high-speed cat ferry and a 63m high-speed patrol boat being the more recent of those.
I should note, however, that you won't see a benefit from simply 'bolting and going' with a set of tabs if the vessel in question is not already sitting heavy aft; in many cases the CG must be moved aft if the lift from tabs is expected to benefit the overall L/D.
