The Chronicler lets us know all of David's military commanders. These guys are the muscle in Israel.
There are 12 divisions in total, each with 24,000 soldiers in them. Now that's a lot of fighting men.
The author also names the men in charge of each of the 12 tribes. That's good information when you need to know who exactly to go see to get the folks from Issachar's tribe in line. In that case, Omri's your guy.
We don't know exactly how many people are in each tribe because Joab never finished the census.
Finally, the Chronicler tells us who does all the other odd jobs in the kingdom. Want to know who's in charge of money, farming, vineyards, trees, oil, or livestock? Look no further.
There are also VIPs: advisors to the king, commanders in the army. These guys are David's (and now Solomon's) circle of trust.