Unlocking an iPhone without a carrier allows you to use it on any network, regardless of the one it was originally locked to. This can be useful if you want to switch carriers, use your iPhone internationally, or sell it to someone who uses a different carrier.
There are a few different ways to unlock an iPhone without a carrier. One way is to use a third-party unlocking service. These services typically charge a fee, but they can usually unlock your iPhone quickly and easily.