You can add and hide columns on the invoice template. You can just simple use check boxes to switch in and out some columns.

Actually we had done this little tweak because some of the clients complained they need explane to their clients why there is a Discount column, but they never get discount. Is there other clients who get discount?

So, in order to avoid such conversations you can now decide whether you have this column or not. I hope this make the tool even better.