When returning from the US to Canada by land, you have the option to return your I-94 to the CBSA official. However this seems to be a bit useless as nowadays all exits are automatically (and nearly instantly) recorded and passed on to DHS, whether or not you return the I-94 paper. Likewise returning your I-94 doesn't reset the I-94 status, so you would still be admitted under your previous I-94 on the next visit to the US.
So the question - does it make any sense at all to bother returning the I-94? Does it change anything at all as far as US immigration officials are concerned?