I believe that this acquisition is more than organizational depth at 3B, which is needed, since the only pure third baseman in the upper levels of the organization is now Deibinson Romero who will probably start the season in Rochester.
A couple of interesting things about Sobolewski (btw, his first name is Robert; Mark is his middle name) : He replaced former Twin Danny Valencia as the starting third baseman at University Miami and he looks a lot like the former Twin with the bat, hitting 18 HRs for the AA New Hampsire Fisher Cats in less than 400 plate appearances, but is much better on the field. He has above average range at third and makes all the routine plays, which was not Danny V's strength.
Sobo (his nickname), is a cancer survivor. He is 25 years old, just like Romero who, also just like Romero, had a break through season in the Eastern league (AA) last season. Sobolewski's defense is slightly superior, while Romero has a better eye at the plate. I suspect that these 25 year olds will provide competition for Trevor Plouffe (something that Terry Ryan wants for some reason) at Spring Training and they will probably start the season in AAA Rochester. It is worth mentioning that both guys are pure third basement and they primarily played there other than a couple of games at second for Sabolewski and at first for Romero.
Sobolewski's acquisition is not like those of Matt Carson, JR Towles, Sean Burroughs and the like of the past season, since, unlike the aforementioned, he has not been a disappointment at the majors and he is just 25, ahead of his prime.
Here is a video of Sobolewski hitting a home run last season: