I haven't seen this mentioned much if at all. Now that I'm grinding through the lower ranks again after the season reset I really notice this in the lower Elos.

Even when people react to things happening on the map they're a little bit too slow, in teamfights they're just a little too late in retreating or engaging. When a teammate gets caught they're just a split second too slow with their CC to save them.

One of the biggest examples is taking objectives (most notably early game dragons and late game Slayer). Even if the team is going to attack it together, you'll always have a few people who want to do something "quick" first (like a jungler wanting to take a jungle buff first). By the time everyone is there and taking dragon the enemy has respawned already and will kill you in higher Elos if you're too slow with making the decision to go for dragon.

The first step is to see information the next step is to process it and make a decision. A lot of people in lower Elos fail the second step even though they are proficient in the first. Making the right decision slowly is as bad as making the wrong decision quickly.