In general, crimp gives mechanical strength and can be soldered for electrical reliability. You can see in Bill's link that the contact has a strain relief crimp for the insulation and a bare wire crimp. This bare wire crimp can be soldered if you wish but is not necessary. Very reliable without solder for automotive use. But it will not "fly".
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
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