Nope, this is not a claim that is supported well. Yes sure there will be a handful of examples, mostly in promotor and enhancer regions, but insertions or deletions in introns and repetitive non-coding DNA will generally have very modest impact on phenotypes and these mutations generally cannot be extirpated by natural selection. That is why the term “junk” DNA is actually not that bad or incorrect in many cases.

If you prefer think of it as “spandrel” DNA in the sense used by SJ Gould.