What is this called (Dash seal???) and do I really need it?

I'm working on a '67 Dart and I took a picture of this "dash seal" before doing paint. I'm not sure of the actual name for these. I took them off before painting and now I can't find them. Do I need them? Should I look harder to find them? I'm guessing they serve a purpose but it's not obvious to me.

Any comments/suggestions are appreciated.

Here is a pic of the driver side.