When walking with your weapon lowered compared to an AI walking with his weapon lowered, the difference in walking speed is quite large. This makes it very hard to stay in a formation if you are not the leader of your squad.

Consequently if you are the leader of your squad, your subordinates will have a lot of trouble keeping up with you over the course of a long route and will eventually get lost if you don't stop and let them catch up.

This also happens with other moving animations, though walking has by far the largest difference.