Many of the cheapest, hackeriest cubesats are deployed into low orbits that decay within weeks or months. Space isn't completely empty, only mostly empty, and even minute air resistance is enough that things like the ISS need to thrust regularly to stay in orbit [1]. I believe it's a common mission profile for cubesats that're built as aerospace engineering senior projects, for example.

[1]: http://www.heavens-above.com/IssHeight.aspx