make a noticeable difference
Something "makes a difference" when it causes a situation to change. We usually use this to talk about positive changes:
Having an extra person around to help out has really made a difference.
Painting the living room really made a difference. It used to be so dark and depressing in there.
A "noticeable" difference is a change that's big enough for you to see and notice. It's not as big as a "big difference" but maybe a little bit bigger than a "slight" difference.