you can use the steam only function of this machine to clean leather, but probably not the best choice.
it has three settings, steam only, steam and water solution and water solution only.
i tried it on my leather sofa, was fine, but i get better results with a damp rag with vinegar and mild dish detergent.
leather milk, like the other user suggested is the better option.
steam can be good to disinfect the sofa and take out bad smells if that is your issue. but you do not need this machine for that.
but for carpets, its top item, i used it on my Persian rugs, both silk and wool, absolutely marvelous results.
upholstered office chair and upholstered auto seats for which its also great. you can skip this if only buying for leather.
but if you had rugs or upholstered furniture its TOP TOP