IaC makes replicating and troubleshooting issues easier: since you can duplicate your environments, you can accurately reproduce your production environment for testing purposes.
In the past, test environments rarely had exactly the same infrastructure due to the prohibitive cost of hardware. Now that it can be created and destroyed on demand, you are able to duplicate your environments only when they are needed. You only need to pay for the time that they are running for, usually down to the hour. Once you have finished testing, simply turn your environments off and stop paying for them.
Even better than troubleshooting is fixing issues before they cause errors. As you refine your IaC in multiple environments, you will gain confidence that is difficult to obtain without it. By the time you deploy your infrastructure in to production, you have done it multiple times already.