This improves the wearing resistance. TCI recommends auto-locking carabiners for main tie ins. The same applies to other nonlocking carabiners. The main purpose of equipment is to protect the climber from falling. You can loose your balance, a muscle can cramp, an insect can sting you, and a host of other events too numerous to mention can occur.
Relaxation is the other ingredient equipment provides.
If you get tired, you can stop and rest while hanging on the rope and maybe get a good picture. You can stop and enjoy it without having to worry about falling. Tree climbing has a unique mind set.