There are a few new key players for the Dallas Mavericks that will play important roles on the team this year. Some of them will be stepping into the starting lineup, like Kristaps Porzingis and Delon Wright. Others will play important bench roles, such as Seth Curry and Boban Marjanovic.
When new players join a team (which happens for every team pretty much every year), there is usually a period of time where these guys need to learn how to play together. This takes place in practice and in training camp, but preseason basketball is one of the best times because it gives them the opportunity to simulate a real game together and read situations.