Originally Posted by Often1

A good TA for business travel, particularly one with access to 24/7 backup will charge either a fee per ticket, per service, or overall. The key is that depending on your compensation, the TA is more knowledgeable, efficient and able to make things happen (they are sitting at a terminal while you are sitting at a gate). They can also be proactive on longer flights by monitoring connections, notifying your assistant if you will be landing late so your assistant can notify business meeting attendees and the like.

All of this goes into the time is money calculation. If 95% of your travel is on one carrier between two airports such as ORD and LAX, not much a TA can do to make that much better. 10 segments including TPAC with multiple carriers in Asia and you will do better with a TA.