Say for example you would like to hide the Estimate Revenue field from the form and make it available conditionally.
Simple script to hide the field would display the form as shown below.
To make sure that such empty spaces are not visible on the form, you can instead create 2 sections on the form, one with the Est. Revenue field and the other without the field.
Through script you can then show/hide the entire section. This way the form layout is not affected.