Clipper is a tool that you can use to keep various peices of text that you copy at one place.
Being myself a programmer, many a times I need to keep many different modified forms of a peice of code to compare and see. Moreover recently, I came across a task that involved not so friendly hostnames and passwords.
So I always had to go back and copy both of them seperately, continuously moving between windows. That was when I felt the need of clippy the most.