Not the parent commenter but

1. Great if you have a wider screen (could never do it on my old 13" Macbook Air, for a 15" it's pretty good but for a 24" iMac it's perfect). But if you need the space youjust have it set to minimize by default, maximize on hover.

2. See the titles of your browser tabs, which is great when you are like me and never have fewer than 30 tabs open at once.

3. Easier to select browser tabs when you have many of them open (ie they don't get squished unreadably small)