Termination of a convolutional encoder vs. state register reset
A convolutional encoder is a finite state machine whose output continues for 
several clock cycles after the input has ended (and of course depends on the input).
What is called a feedforward encoder typically has a FIFO buffer through which
the input data bits progress and ultimately fall off the end. This part
of the encoder output
has valuable information (parity checks on the data bits still in the buffer)
that the decoder uses in correcting errors at the receiver end.  Thus,
resetting the encoder to zero state right after the last data bit has entered
the buffer is not a good idea. It is better to pump in zeros until the
last data bit has fallen off the end of the buffer (and to transmit the
corresponding encoder output bits to the decoder for use in the decoding process).
For a feedback encoder, there can be issues with poorly designed encoders
in that the buffer may never empty out, but such encoders are rare in practice.