The main impact you will face is that at some point, you will be compelled to update to a version of UiPath Studio that has removed support for these workflows, in the meantime you will not be able to leverage new features as they will not be designed to have Windows-Legacy support.
I strongly urge you to start migrating these processes, you need to do it at some point, its worth doing it as you go as you do any maintenance work on these projects and keep a list of them where you can do others when you have down time.