Timing can matter in two ways:
Firstly if multiple clocks need to be resolved. See Brian’s comments here. As soon as a clock-drift compensation mechanism is introduced then the receiving unit is not getting a bit-perfect stream.
Secondly, jitter. This article on Bit Perfect Jitter from the Well Tempered Computer site explains how it occurs and the differences it may make.
Noise from power supplies etc. can be carried by earth wires and affect the receiving unit, without ever being encoded in the signal. This article from the Well Tempered Computer site sets out how such noise can affect a bit perfect stream.