Conditional fields would be nice. Let’s say I have a checkbox and if checked, then additional fields appear for filling in.
Another example: I have a database of clients with their billing addresses. But if their physical address is different, I have to list that as well, but not all of them have this, so it would be nice if those fields only appeared when (for instance) the “different physical address” checkbox was checked. This is also nice as you do not have a bunch of extra fields blank when printing.