I was lucky to work for airlines that were quite reasonable even after 9/11. Yes, we had to advise the fleet office and get an OK from the other colleague, but we could still take family, which enabled me to show my parents and siblings what a normal four sector day means. Sadly, around 2015 things got more complicated and difficult, the last freedom we had was taking ATCOs and pilots (badge was required from either group) from other airlines on the jump seat and eventually that was taken away as well. As far as i know there are still some airlines that allow crew from other carriers on standby tickets, but as i don’t have standby travel anymore (the perks of flying low cost) i can’t say from first hand experience if that is true.