The major difference is you can use the LSL as normal cargo vessel during peace time, with 2 derricks and one crane to load and unload heavy cargo, and the beaching equipments for wartime use. It should be noted that those vessels were being ordered by the Ministry of Transport of UK and operated by British-India Steam Navigation Company at the early days, thus emphasizing their logistic ability.
Of course, most nowadays amphibious vessels are equipped with at least one or several cranes also