You can own a range of cogs cheaply, change them easily, quickly and with a small, light tool everyone has.
Servicing cassette hubs is easier than servicing screw on freewheels and the parts are common.
They're better sealed and lighter.
You can tune your chainline if you want.
You can run a couple of cogs at once.
And your rear wheel is interchangable with other bikes and the whole world of road cycling.
You can own a range of cogs cheaply, change them easily, quickly and with a small, light tool everyone has.
Servicing cassette hubs is easier than servicing screw on freewheels and the parts are common.
They're better sealed and lighter.
You can tune your chainline if you want.
You can run a couple of cogs at once.
And your rear wheel is interchangable with other bikes and the whole world of road cycling.