It depends. There are situations that demand an immediate call to the IG. These are usually pretty cut and dry. They tend to be serious offenses that involve a member of your Chain of Command. Let’s say you believe your 1SG is having an affair with a spouse in the unit. You could take this to the IG or to the BNCSM/BNCDR. Both of these would be equally acceptable courses of action.
So what about less serious problems?
When a Soldier goes to the IG, the IG gathers information and then contacts the command group at the appropriate level. When the command group resolves the issue they report back to the IG with the action taken. The IG does not direct the chain of command on what action should be taken. There are exceptions to this but they are rare and deal with very serious matters in which the chain of command has refused to take appropriate action.
Soldiers should use the IG when they believe the Chain of Command has failed them. With that said, remember that your chain of command may have acted appropriately even if you feel wronged. If your Chain of Command did something inappropriate, the IG will expect proper action to be taken. If proper action is not taken, the IG can refer the matter to the next level of command or advise the commanding general on a recommended course of action to resolve the issue.