The separate arrivals and departures routes at Kings Cross is a mess. Initially, after the restructuring, if you tried to enter the (obvious) front of the station from the road/buses, there weren't just signs saying it was the exit, but a barrier line stopping you from cutting through to the departures area that way. That was so silly that they had to put a kink in the gate/barrier line so you could get "legally" from the covered space along the front of the exit gates through to the departures area. It's an obvious "desire line" and loads of people go in that way despite signs saying you should go out and loop round the back of the underground access steps and in the "proper" way. [There is a possible physical way through from the front of the exit barriers to the outside of the "official way in", without going out and round the underground access in the weather - but it's sealed off!] In any case, the gates are open for a lot of the time, so the exit concourse inside the gates is a common cut-through to/from the departures area and the street in front of the station. I have no idea what would happen if the gates were put back into use while making that shortcut (rather than making the wiggle they've introduced at the end of the gate line), I guess you'd be hassled for not having a ticket. (It's never happened to me yet, though.)
Another issue for arrivals is trying to meet someone there. If you arrive on a train and don't know the place, your only obvious route (leaving aside the separate suburban platforms) is to go straight out of the gates, a few paces under/across the "arcade" and out into the street and the weather. Whilst someone meeting you is going to be across to the west side, out of sight in the "departures" area - not only because there's nowhere civilised to wait at the official "arrivals" barrier, but (incredibly) there's no arrivals information visible at the arrivals barriers... you can only check arrivals from the departure area!
The original idea for people catching a train seemed to be that people in the departures area would, after entertaining themselves in the shops, take the escalator - which is well tucked away - to the upper level (with more shops!!) and then go round that walkway, though a passageway through the wall of the main train shed, where there are a couple of ticket gates, and on to an overbridge, and then go down onto the relevant platform. Nice on a planner's design perhaps, but counter-intuitive, sending you on a circuitous route, away from where you can see at least some of the platforms (from the southern end of the departures area). Whenever I've been at Kings Cross (which is virtually next door to where I've worked for years, so I'm around the place all the time - mostly not for train travel purposes!) I've seen almost no-one use that high-level access to the footbridge down to the platforms. People go via the gates at the southern end of the departures concourse, heading across the front of all the platforms until they get to the right one, intersecting all the arriving passengers at right angles.
When the design was first public, some of us pointed out it wasn't sensible in terms of actual human behaviour - to no effect of course, apart from the kink in the gateline which was only introduced after they'd realised that the people who told them so were right all along.