# Physical significance of Don't cares in Digital Logic design

In many Digital functions we come across don't care conditions where we use don't cares to minimize functions.
What is the significance of these don't cares in real world scenario where we actually implement the functions using logic gates?

• The don't cares give us more freedom in implementing the logic. This allows smaller and faster logic. – Yuval Filmus Oct 22 '16 at 18:26

Each don't care bit represents 2 values {0 or 1}, hence a function containing 'k' don't care bits correspond to a class of $2^k$ distinct functions ( as 'k' inputs can give rise to $2^k$ combinations).
The task is to choose a function out these $2^k$ functions which has the most minimal representation. Thereby decreasing the number of inputs hence making the implementation faster.