What is that black pod on the left wing of a TBM?
That is the front of the housing which encloses the 10" GWX70 Color Weather Radar antenna.

Here are some close up shots of a TBM depicting the weather radome. 


Source: Own work

Note the lightning diverter strips:


Source: Own work

Apart from the simple fact that airborne weather radar is useful, weather radar is a common option due to the equipment requirements imposed on air carriers operating such aircraft. Specifically, in 14 CFR 135.175, the FAA generally prohibits operation without airborne weather radar equipment along routes where thunderstorm activity is forecast.

Many such single engine aircraft include the option for wing-mounted weather radar, as seen on the TBM 900 in the original question. Since weather radar requires a relatively unimpeded area for signal transmission and receipt, the antenna assembly is typically located at the nose of the aircraft, such as on most multi-engine aircraft. In aircraft with nose mounted engines, a mid or outboard wing mounted position makes sense. See the following photos depicting examples of wing mounted weather radar on a Piper PA-46-500TP Malibu Meridian and a Cessna 208B Super Cargomaster, and a nose mounted weather radar on a Beechcraft King Air B200, respectively:   


Source: Own work


Source: Own work


Source: Own work

According to the TBM 900 POH, installation of the optional radar system results in a 5 KIAS decrease in maximum cruise performance and a 3 KIAS decrease in long range cruise performance. This change is due to the slight increase in drag from the radar antenna housing.