I'll just echo the comments already made. It really depends on what YOU want to get out of it. The bare minimum would be to download the new file, tweak your lineup and export it again.
I on the other hand am in only one league (the one I commish) and I am looking at it constantly. I go over every box score my major league team plays. I look at the stats by week for all levels of my organization, and I micromanage the lineups and pitching staffs of all levels. I check the statistical leaders, the attendance figures, the team stats for every team in the league each sim. Then I look ahead to my next week and try to get my lineups set in the best manner possible against the projected starters of my opponents, but thats just me.
Here is the link to our league.
NARBL