Bashing Focus is a star within the Constellation The Tower in Elder Scrolls Online.
With each point invested, the reduction in the Stamina cost of Bash attacks diminishes. That is to say, for the first 10 CP invested, you would gain a 6.7% reduction in Cost. However, the next 10 CP spent (making a total of 20 CP spent), will earn you only 5.96% more reduction. This is 0.74% less than the reduction gained in the first 10 CP.
As such, spending just 37 CP into Bashing Focus will already gain you a 21.15% reduction in the Stamina cost of Bash attacks. This means you will have gained 60% of the Maximum reduction possible (which is 35.0%) by spending just 37 out of the total of 100 CP. Therefore, beyond this point, the reduction in Stamina Cost received per 1 CP used is very small and not as worthwhile.