Though most people don't use them there are plenty of hiding spots that only exist on one side of certain maps. For example, on gullywash mid there is a light you can stand on as roamer in order to force meds coming in from one 2nd into mid (IIRC it's red) which technically gives blue side an advantage. On badlands as well there are a couple of spots that exist on red second that aren't mirrored on blu side. In house there is a hiding spot above the door frame by window room/entering the health pack room with a prop of like a ram's skull or something. Way above patio by choke on red 2nd you can stand on a prop and see through walls all the way to blu diag/house (more of a glitch than anything useful) and since nobody checks up there it's pretty easy to force medics coming through choke and if you do it right you're so high up that you can sync rockets on him. Obviously if the map makers were to do their jobs right and mirror the maps properly it would be a non issue but as it stands that we have a halftime in NA I see no reason not to switch sides because it's only fair. Also I think it may be from maps like gravelpit where switching sides is customary.
Edit: also I completely agree that in anything other than an esea lan with 4 teams (rip) the esea ruleset is simply too time consuming. I would argue that in single online matches its better than having just one 30 minute half (you can use halftime to check stats) but obviously in playoffs it becomes really time consuming especially in best of 5 games. No idea how the EU map rotation works could someone explain how there are two maps played each week? Sounds like an interesting idea.