9-32T vs 9-42/6T 9 Speed Cogs

The larger tooth count sprockets will provide lower gear ratios. Bigger sprocket in the rear: lower ratio. A lower ratio mean the bike goes slower for a given pedalling cadence, but you get more torque at the rear wheel.

A larger largest sprocket also means the ratio gaps between gears get bigger - the intermediate sprockets all get proportionately larger too.

You need to optimize you gear ratio spread for the type of riding you do and on what terrain. If you are commuting on road without big hills you probably would benefit from a narrower range cassette without very low gear ratios. If you are looking for higher gear ratios to allow you to go faster without having to pedal too fast you need larger chainrings on the crank, but beware, it's often impossible to install bigger chainrings on an MTB due to crank compatibility or chainstay clearance problems.