Certain situations require a person to think through what they should do before they act, because if they were to go by instinct, they could become careless and something could go wrong.
Other situations require more of a gut feeling. To just do what you have to do at the spur of the moment. For me, this usually centers around giving certain types of advice to friends and family, I do or say what's on my mind as it goes into my mind.
I personally think that it's best to have an equal balance of the two things. But I guess I usually think things through more often than I go by my gut feelings. I dunno, I guess decide on how I feel about a situation, and then think it through from there.