For maximum benefit, you want to do a pressure flush to get not only the old, potentially moisture loaded fluid out, but also any debris from degenerating rubber components. The fluid needs to be dry and particle free to maximize the life of the AGS system. Really cheap insurance. Now, if you lived in the high desert versus near a sea shore, you might be able to stretch it a bit, but still, it's cheap insurance.
2014 i3 BEV, 2021 X5 45e
(The i3 will be sold soon, <17K-miles, interested?)