Without the exchanges and their subsidies, far fewer people would be subject to both the individual and employer mandates. Had the IRS not unilaterally extended to the federal exchanges the subsidies that the language of the law only extends to state exchanges, those individuals and businesses would be free of the mandate.
In Halbig v. Burwell, a group of employers and individuals sued the federal government, arguing that the IRS regulation contradicted the plain language of the ACA as passed by Congress and signed by President Barack Obama.
Two members of a three judge panel on the Appeals Court did a very simple thing: They read the law and the IRS regulation. They then determined the regulation did something the law did not authorize: It provided subsidies to people buying insurance on the federal exchanges.