PSA: AFKers hurt your team even more in preseason
"If your team's average level is higher than the enemy's, your minions deal 10% bonus damage to enemy minions. If you've taken cumulatively more turrets than the enemy team, damage is further increased by 10% for each turret you have over your opponents."
Not only does an afker already put more champion pressure on every lane, but now they will be giving their opponents additional pressure from the minions by automatically dropping you team's average level. After that there is the fact that the enemy team will take at least one turret far earlier as well.