an extra pull behind off set mower with engine. if you are cutting open fields. it can reduce mowing time. by providing an extra deck per say, beyond deck current attached to regular mower / tractor / zero turn.
Swisher 5 " Mower
Swisher finishing lawn mower
trying to push to the "ultra wide" 72" plus mower decks were it is a single deck = SCALPING the dirt, even a little bit of 1/2" difference if that, will cause the deck to bounce up and down at different corners, causing uneven cuts, and more so scalping.
when you start getting up there in width, most manufactures will start going with "multiple decks", to reduce scalping, and create a more even cut.
then you get up into "gang" mowers. were they offer 3 or more decks. stay away from "reel" mower gangs. they do not really handle tall grass very well.
allis chalmers CA tractor with narrow front end (think three wheeler almost), 1954 tractor 20hp gas, she an old tractor, and about 7 acres to mow. but she goes through tall and thin grass like crazy, granted i have a lot of hills, wet spots and dry spots. and the R1 rear tires can be needed at times. it has 59 inch deck on it. 4 gears, and if possible tend to mow in 3rd gear. which is around i want to say 5 MPH. the over all ground speed is a must, also the old tractor does not give you the "vibration effect", smaller riding lawn mowers you hope on them for a couple hours, then got off, and feels like your body still vibrating. it has its issues, and you need to keep up on pre-maintenance on it. but other wise runs nicely.
the difference between the old allis chalmers ca, vs a riding lawn mower at local stores. = 2 riding lawn mowers = one old allis. as far as time amount in mowing. that is ground speed, plus HP to keep the blades spinning and gong faster at the higher ground speed in taller grass.
when you get into small size zero turn mowers, the decks may not lift up as high, and may not have enough HP to keep them going resulting in more "half passes" (mowing only half the deck width) when grass gets a bit to tall. granted it is the same for smaller size ridling lawn mowers as well.