A finished hairline gives you a very nice hairline by covering up the edge of the lace. This process is called Under-ventilating.
With this type of hairline, you're basically limited to only wearing it behind the hairline. You can't glue it down because the ventilating across the free edge will not stick.
This type of hairline is great for adding combs across the front. If you are wearing your natural hair out to conceal the edge, this hairline would be great. Normally a thing foundation is placed underneath to conceal the edge of the combs.