Google+ keeps changing it's layout but it looks like it's stable this time. It's still important to have a unique cover photo if you have a business. Here's how mine looks like:
I demonstrated what I'm all about and what they should expect from me. So if you decide to create your own, be creative!
The new Google+ cover photo size is 2120px in width X 1192px in height. Covers should remain at 16:9 and the minimum size should be 480px X 270px.