The Box to Box can be seen as a combination of CM(A) and CM(D) without the hold position PI. He requires a lot of acceleration and Stamina to even perform his role in an effective way, which is why it is a depreciated role for lower league sides.
The CM(S) is a lot static than a Box to Box, instead of a combination of CM(A) and CM(D), it's more a compromise on both ends. The CM(S) won't get as high up the pitch as a CM(A) or B2B, and wouldn't come as deep as the CM(D) or B2B.
Tactically speaking, with a B2B you get one extra player on the field. He often arrives late into the box and provides great penetration options for your playmaker. In an ideal scenario, you are imagining a player who will win the ball back in your own half, pass it around and then score the goal. However, since he is expected to be on both sides of the pitch he might be at the wrong end at times especially if he has a poor decision, acceleration or pace rating.
On the other hand, this is CM(S)'s greatest strength. You can always expect him to be near the centre. When your team is attacking, he will sit outside the penalty area and look to regain possession from opponent's clearances. On lower mentality, he will be a very good back pass option and will help you keep possession. And when you regain possession, he can act as a pivot and help you get the ball to more attacking players. The CM(S) is also a good choice if you want the creative abilities of DLP(S) without asking the rest of the team to pass to him.