Not much to say I guess. I am sure you could make do with an old cut-down bucket or something but when you are dealing with an oil change in your own garage you should be collecting all that dirty oil in something less likely to tip over and spill everywhere.
Hence, this allows you to drain your car oil with more practicality. Plus, if you are servicing your own car on a Sunday with the garage door open you are going to impress your neighbours a great deal more if you have all the right kit to do it, right?