The two are interwoven. In the past I was never one to set goals. I just wrote when the inspiration struck me and finished my work whenever. That was in the blissfully pressure free 'before'. Now that I've decided I want to make a career out of this writing thing I realized I was going to have to step things up.
Setting goals for yourself now, long before you reach the publishing stage is like preparing for the battle. You won't be ready if you don't do it. If you sign on for a three book series they will likely be expecting a book from you every year. Can you write a book in a year, can you write a book in six months? Chances are if you never set goals for yourself you may not know. Trust me, you want to know the answer to that question before you plunge into the river.
A friend of mine missed their deadline for their sequel. Publishers don't like this, it throws off their entire plan and can cost money and effect sales. Upsetting a publisher is like jumping in the river to get a close up of watching pirahnas feed. It can go horribly wrong.
So now I set goals for myself; at least two pages a day. Two pages a day guarantees you'll get your book done in a year. Unless you're writing the next War & Peace, in which case you'll need much better advice than mine! But if two pages a day is too daunting considering your hectic life, don't sweat it. You don't have to be that industrious in the begining. Shoot for a paragraph a day if that's all you can get. The point is to start setting goals and meeting them so you're already well practiced at it for when the time comes for you to meet deadlines. Time to practice what I preach and write something!
Best of luck!