It can help..and it can hinder. It helped me in the sense that I was very comfortable with the patients, talking to them, caring for them etc. it was a hinder for me because I was, for a while, stuck in the CNA mindset.
CNA's sometimes keep that mindset that they are a CNA and act as such. Meaning, they are reluctant on doing something without the "ok" from a nurse or asking the nurse what to do. Do you know what I mean?
For example, I found one of my residents during clinicals with edema to her bilateral ankles. Now, obviously I knew to elevate her legs, check for any redness or pain etc. But before i did anything, I went to my instructor and told her what I found..she said "and you did what?" I told her I came to her. She said you are a nursing student, you need to think like the nurse and act upon it. (obviously within reason).
CNA experience behind you can be helpful too. But being a CNA doesn't make you a better or worse nursing student. I had several students I went to school with who had ZERO CNA experience, some had no medical experience, and they were great in clinicals, and are very good nurses now, I had students who were great CNA's but terrible nursing students, had some with no CNA that were terrible and had some CNA's who were great..