what is a maverick?

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i'm curious about this word, as well as wondering why being a maverick is supposed to be a good thing for a president/vice president to be in this day and time, facing the problems this country faces.

from good old dictionary.com:

mav·er·ick /ˈmævərɪk, ˈmævrɪk/ Pronunciation Key - Show Spelled Pronunciation [mav-er-ik, mav-rik] Pronunciation Key - Show IPA Pronunciation
–noun
1. Southwestern U.S. an unbranded calf, cow, or steer, esp. an unbranded calf that is separated from its mother.
2. a lone dissenter, as an intellectual, an artist, or a politician, who takes an independent stand apart from his or her associates.
3. (initial capital letter) an electro-optically guided U.S. air-to-ground tactical missile for destroying tanks and other hardened targets at ranges up to 15 mi. (24 km).
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[Origin: 1865–70, Americanism; after Samuel A. Maverick (1803–70), Texas pioneer who left his calves unbranded]

—Synonyms 2. nonconformist, independent, loner.

looking at definition 2 above, does a maverick listen to his or her associates? does a maverick explain the basis of his/her reasoning?

it seems to me that sometimes being a maverick could be a good thing, as in being able to think for oneself, and it could be a bad thing, as in making risky decisions without being accountable.

i guess it's up to the crowd to make the determination. is a maverick a good thing for a presidential candidate to be? are there other presidents who have been considered mavericks? and how often does one have to dissent from his/her associates to be labeled a maverick?