In the years before, tailors would fold the excess fabric at the bottom of the legs, and iron / stitch these into rolled fold-overs called cuffs. Their main purpose was to make sure that trousers bottom wouldn’t get dirty and hold their shape despite the movement.
Over the recent years, advancement in fabric design and tailoring have led to a modern version of non cuffed trousers which are finished off above the shoe so as not to get dirty, and eliminating the need for the folds.
Generally, pleated trousers are wider leg and worn with cuffs. Slim fit trousers are preferably worn as non-cuffed trousers.