You can type /w username message to message an online friend. If your friend replies to the initial message, you can just type /r message/. If you want to send another message without a response, you have to use the /w method again.
The /r method will automatically fill in the username of the friend you are having the conversation with when you start typing the message. (It fills it in with the last user that messaged you)
/w = whisper
/r = reply
They have to be on your friend list as well as in the same region as you for this to work.
If you have a friend that thinks it is fun to spam you during a match, you can use /mute username, which will stop chat for your game's duration. I would not recommend using /ignore username as it will remove your friend from your friend list.
Honestly, this has nothing to do with auto attack on or off. Or standing still for that matter. You can be constantly moving, but not be applying the side step or animation canceling technique.
There are 2 main reasons why would you would do this side stepping as you would call it.
In both Dota and Dota 2, there is a mechanic called animation canceling. When your hero attacks a unit, the damage gets inflicted upon the unit before the animation is finished. So by side stepping really quickly, and then attacking again, you are able to cancel the ending of your first attack animation and then proceed to initiate another attack animation. This is widely used in the jungle as it increases the number of attacks you can deliver in a specific period of time.
Another reason to do this side stepping is positioning. For example, let's say you are on radiant side, and at the bottom of a creep wave. But perhaps you want to be north of the creep wave and take an offensive position, while pushing the wave. The most efficient way to keep the pushing at a maximum is to hit a creep, animation cancel by taking a step forward and repeat.
EDIT: For melee heros, you side step after the damage is inflicted. For ranged heros, you side step after the projectile is released.
Best Answer
There have been concessions in professional LoL. The most notable example I can think of is at IEM Katowice in 2016, Fnatic conceded at 22 minutes to SKT T1 during game 3 of a best-of-5. It generally happens at tournaments where there's a massive skill difference and the losing team concedes out of fatigue. In the case of MSI, Fnatic was on their 4th Bo5 in two days and knew they were hugely outmatched so they conceded instead of drawing out an exhausting, losing game.
Mentality plays in part. It's seen as poor sportsmanship by some, most fans want to see it play out and hope for a huge upset rather than a team conceding out of poor morale. Comebacks and backdoors are frequent enough in League that teams and fans will still feel like there's at least some chance and try to play it out. C9 vs Samsung Blue at 2014 Worlds is a good example of this. C9 was clearly outmatched but they played out the entire series in hopes of getting an upset.
I've only played a few games of Dota in my life so I might be wrong here, but it seems that games end much faster in League than Dota. Cracking a base and killing the Nexus is much easier in League. In the few games of Dota I played, it took a long time(5-10 minutes) to crack the base and get onto the Ancient/Nexus/Immortal. In League, teams can break into a base in just seconds after a wipe if enough survive the teamfight. So it makes sense that if you're being sieged in your own base in Dota, you'd concede instead of drawing out a long closure, while in League it's so fast you might as well play it out since you won't save much time. This is all pure conjecture though, I'm not that knowledgeable about pro Dota.
Another point thanks to @Cronax: comebacks are FAR more likely. In the late-game, even if the enemy is beating on your Nexus, if your team can somehow manage to win the teamfight and kill them all, this can give your team enough time to kill the enemy nexus instead.