  Entanglement subject to noise can not be shielded against decaying. But, in
case of many noisy channels, the degradation can be partially prevented by
using local unitary operations. We consider the effect of local noise on shared
quantum states and evaluate the amount of entanglement that can be preserved
from deterioration. The amount of saved entanglement not only depends on the
strength of the channel but also on the type of the channel, and in particular,
it always vanishes for the depolarizing channel. The main motive of this work
is to analyze the reason behind this dependency of saved entanglement by
inspecting properties of the corresponding channels. In this context, we
quantify and explore the biasnesses of channels towards the different states on
which they act. We postulate that all biasness measures must vanish for
depolarizing channels, and subsequently introduce a few measures of biasness.
We also consider the entanglement capacities of channels. We observe that the
joint behaviour of the biasness quantifiers and the entanglement capacity
explains the nature of saved entanglement. Furthermore, we find a pair of upper
bounds on saved entanglement which are noticed to imitate the graphical nature
of the latter.
