Is passing array as GET parameter a security issue?

I college of mine just denied passing repetitive values as a get parameter because it was a security issue. I google the term he mentioned "parameter pollution", but that is the first time I am hearing of this. Is it really a thing we should be concerned. I am working on a ASP.NET MVC project but it doesn't matter - this question affects all web frameworks. So is passing an array as a get parameter like ?key[]=v1&key[]=v2 wrong and if "yes" - how.