The value is pretty similar to autocomplete in that sometimes it's more efficient than manually typing everything out. Sometimes the time it takes try select the right thing the complete would take longer to type manually, and you do it that way instead, and sometimes what you want isn't even going to be something you can autocomplete at all so you do it manually because of that.
Like autocomplete, it's going to work best if you already know what the end state should be and are just using it as a quicker way of getting there. If you don't already know what you're trying to complete, you might get lucky by just tabbing through to see if you find the right result, or you might spend a bunch of time only to find out that what you wanted isn't coming up for what you've typed/prompted and you're back to needing to figure out how to proceed.
Like autocomplete, it's going to work best if you already know what the end state should be and are just using it as a quicker way of getting there. If you don't already know what you're trying to complete, you might get lucky by just tabbing through to see if you find the right result, or you might spend a bunch of time only to find out that what you wanted isn't coming up for what you've typed/prompted and you're back to needing to figure out how to proceed.