Instant File Initialization is especially helpful when large file growths are occurring. Without Instant File Initialization, SQL Server has to write zeros to the disk in order to initialize it before SQL Server can use it for new data. As with autogrowth, the amount of time this process takes depends on the size. The more disk space that is needed, the longer it’s going to take for the disk to be zeroed for use. Fortunately, IFI exists to skip the need to write out zeroes. Instead, disk space can immediately be used as needed.
IFI can also make a noticeable difference when restoring databases. If you’re working on getting your recovery time objective (RTO) down, check the status of IFI. Enabling IFI may help cut that number down to an acceptable value.
This is particularly interesting because, for the most part, I’ve only seen posts showing how to enable it at installation time.