You need a portion to lock the crotch in place like so:
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"Think about a character running: if there's no loop of polys in the crotch seperating the two legs, when one leg goes forward and the other backward, they're going to be pulling on each other, resulting in horrible deformations and shading. That loop of polys acts as a buffer zone- it wants stress to be put on it, that's what it's for! Not to mention, it's anatomically correct. If there's no loop of polys existing between the legs, the character has no genitals! Yikes!"
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Be sure to check ancient pig's tutorial for other useful tips on the subject.