A few months ago, I switched to a 13" Macbook Pro from a 27 inch iMac. I love it and am more comfortable with the smaller screen than I ever thought I would be.
Now, with El Capitan, we're able to hide the Menubar, which saves 23 vertical pixels. Even those few pixels really make quite a difference, I've found.
Logos' top menu is an area that could use some trimming:

Here it is, alongside Safari, the icons are roughly the same size, but the space is more efficiently used. I think 10-20 pixels could be trimmed without losing any "clicking area."
Not complaining, but just suggesting that some space could be better used.