The reserves around Trafalgar differed from the light forces held away from Jutland. Additional British fleets in the Channel in 1805 were still enforcing close blockades of French ports and formed successive barriers if the Franco-Spanish fleet escaped Nelson. The Harwich Force had no equivalent blockade station tying it down in 1916, so keeping it back did not serve the same strategic purpose. Sending it north would probably have cost ships, but concentration at the decisive point could have trapped or delayed the High Seas Fleet for Jellicoe.
Notable Point · 1:18:48-1:19:39
Trafalgar's reserve logic did not fit Jutland
British squadrons behind Nelson in 1805 still had close-blockade duties, unlike the uncommitted Harwich Force in 1916.