So this tab width is dynamic, the benefit is being able to say that perhaps all tabs will have 20px padding on either side of the label. Avoids wide tabs with small labels ( if that is a terrible problem).
All these tabs are the same width, benefit is they all have even placement, and weight for the most part. The issue arises when you might have a long label...that won't fit the tab, I suppose just being judicious with labels will solve that.

