How much money do you have to spend on your release? Do you have skills in cover design, formatting, editing, proof reading, social media marketing, or promotion? Do you have connections with bloggers or reviewers, or understand what you'll have to do to grow a fanbase? How many books are you planning on releasing? How fast do you write? What genre are you in?

Self publishing is more than just hitting publish on a book. It's a lot of various skills that require a lot of time -- or money, if you want to hire it out to others. Having a professional team behind your book could be an absolute boon, and publishing through Penguin could give you a lot of respectability in certain circles.

I exclusively self publish right now, but I'd say only 10-20% of my time is spent publishing. The rest is handling all the marketing, promotion, graphic design, formatting, web design, etc. that self publishing requires.