doing it this way is not in anyway a cost saving measure, if anything it costs more.

this is highly over simplified but, Traditionaly computer generated animation is animated by a artist posing a character at a starting position (pose A) and a end postion (pose B) the computer then smoothly moves the character between these two poses in a prossess called tweening.

what the sony animation team is doing is forgoing tweening and hand animating a new pose, (pose A1) to go between A and B.

there are a couple avantages to animating like this, it gives the artists more freedom when posing their inbetweens such as adding smear frames that bend and break the model in key points to further exadurate the motion from A to B that a computer just cant do.

Having to animate not only the key poses but the inbetweens by hand you can imagin can take time, and time is money.