I can't say I've done a clip test either.
You would do a clip test (or snip test) if you have an important roll of film that you don't know how it was exposed. Like you inherit your grandfather's camera and find a roll of film in it. You might have pictures of your grandma as a young girl but don't want to take chances.
A more routine situation is doing a film sensitometry test. You want to develop short sections of film for different times. Each test is about six inches of film, and you want to develop it for different times like 4, 5, 8, 10, 12, 16 minutes.
In 35mm reels, development already varies between the outside, center, or in midsection of the roll of film.
True a test strip won't "use" the developer the same as a regularly exposed roll of film. The agitation will be different if you aren't using a whole roll of film too.
But I don't consider these variations critical, I mean I don't think they would cause a 5% change in results.
I personally just "expose" a sensitometry test at the end of a roll of film that I rewind early. I just run my tests in with my regular film runs, as a process control.