Strops are required to keep your straight razor's edge keen for daily use, they do not 'sharpen' as such, but rather aligns the edge for a smooth and comfortable shave. Strops can play an important part in the actual honing process, as they will remove burrs of razors freshly honed on whetstones, a very important step for any sharpened instrument. They can also be use for honing and improved blade retention when used with abrasive pastes, sprays or other compounds. Using cheaper leather for the latter is advised, as you'd always need a 'clean' leather strop for daily use, once you have used a specific spray or compound on leather, it is advised to stick to using only that specific compound on the strop. Essentially shavers normally end up with a few good strops that they keep clean and care for very well, but most also have a few cheaper strops or pieces of leather used with compounds and sprays.