I haven't done it but I've given it some thought and have tried to talk my wife into coming along for a long overnight or a lost day (There's a lost day in SPI in open time right now that would be a good one if the flights are fairly open going both ways for your spouse).

MOST of the time, there's room in the hotel van and I don't see how it would be a problem as long as there is room for the extra person. Otherwise, you'll be looking for an uber or taxi.

Also, regarding your return flight, your seat is not only guaranteed, it's required. Your spouse's seat is not. Your spouse probably needs to be independent enough to deal with the situation where they don't get on the return flight (and even perhaps figuring out the hotel and transportation needs if it means staying another night on their own) and be cool enough to not blame you as you taxi away for takeoff.

I've never seen someone actually bring someone though. A flight attendant once tried to bring along her husband but he didn't get a seat on the outbound flight so he was left in base.