Two hours at LAX is plenty. The DL terminal is pretty small, compared to other similar sized airports. I honestly would say it's not worth it and I have used the service often. It would make things a tad bit easier if your gate happens to be out of the TBIT, but thats increasingly rare with the new T3 gates open.

It's most helpful to me with tight connections (under an hour) or arrival service, assuming you have a driver picking you up, as it's truly spectacular to be taken off the plane to a Porche and have your driver waiting for you in a secure area, without needing to deal with the terminal at all or wait for your bags in baggage claim.