I see some players use their left hand thumb more at the side of the neck. The baseball bat grip so the say. Especially when playing low notes on the E or even A string. I am not talking about amateurs here but players like Chris Minh Doky, Charlie Haden and even Christian Mc Bride use it sometimes. Some players more than others but I see it fairly often with jazz players or other 'lighter' genres. It can't be because of bad technique. Is it because it gives more strength or is it because of sound? I started as a classical player so I never use it myself. But what are the advantages?