Get rid of any and all forms of "You can’t"
Something that has been annoying me gravely while playing the game, is the “You can’t do X because of Y” notifications. For example: You can’t remove an airplane stand which has boarding desks connected. This basically means that the game forces me to manually remove all connections (which could be quite a few when using auto-boarding desks). This can easily be replaced by an “Are you sure you want to remove this stand? There are still boarding desks connected” notification, or something in that direction.
The same goes for the Delivery Site. I’m not 100% sure if that’s only used for construction materials or not, but even then, a notification saying “Removing the delivery site will prevent deliveries of construction material, X and Y. Are you sure?”. Since it’s such a critical part of the game (at least when playing with construction on), you could add a permanent notification on screen until a new site has been placed, to prevent the “tHiS GaMe iS bRoKeN” posts everywhere.
Any and all forms of “you can’t do this, you need to do that first” takes the flow out of the game. I think that in pretty much all cases, a simple yes/no question can completely replace the warning + manual action. If you click yes on deleting an aircraft stand, it makes complete sense that the boarding desk connections get deleted for example.
Why it should be implemented:
A “you can’t do this” popup takes you out of the flow of building something (especially when it also takes you out of the tool, like it does with the bulldoze tool when hovering over the delivery site), and they can easily be replaced by simple yes/no / ok/cancel popups, which could potentially be switched off in the options, for more experienced players.