In 4040 Baseball, the GM has the same mission as in real baseball:
There are 30 GMs, and each of them has his or her own unique profile. That profile governs everything from when the GM likes to make trades, to what type of players the GM finds most appealing, to how finanacially liberal or conservative the GM is when building a team.
Each GM drafts players from the amateur pool based on his or her prefered player types. For example, a GM might be most interested in developing power hitters, with a secondary interest in pitchers with high strikeout rates. Another GM may prefer contact-first hitters and pitchers with elite control. Yet another might lean toward speed and defense as priorities.
During the draft, each GM will draft according to those priorities.
The league days are played in cycles of five days in the morning, and five games in the evening, or 10 league days per day. Before each set of five day cycles, each GM reasses the team roster, and promotes, demotes, signs, or releases players.
As a result you may see changes in SIM team rosters over the course of the season
GMs participate in trades in two ways:
Additionally, each GM has their own windows for when they will trade. One might only trade before the season begins, and at the deadline. Another might trade only after they've gotten a look at how their team is performing.
GMs are motivated to trade players for a number of reasons, including:
GMs will not trade with division rivals, and once the deadline is looming, they wil also avoid trading with potential playoff rivals.
More about trading with sim teams.