I use it for two things.
1/ guess my game shape sublevel. I record my base DMI the first week of the season when GS is reset to 7. Then by conparing my weekly DMI to the base value or to the previous week value I can see wether my GS is 8(high) or 8(low) for example. When it is close to th evalue for GS 9, it's mean GS is 8(high).
2/ To asses the strength of opponent players. Early in the season you can use the salary. But later in the season if the player was trained is printed salary could be far lower than it's current value. As DMI is based on the virtual salary, it takes into acount training since the sason begining, so it gives a better picture of the player strength.