Levelling here doesn't require you group with other players 99% of the time, you can level up really quickly by doing solo quests, and even some dungeons solo, in a matter of a few days playtime really.
Most games that have been running for a long time, even retail servers, have fairly empty maps until you reach the high levels. The only time they were really packed with players is on launch day. I played a couple of large retail games recently and didn't see a single soul outside of the towns.
However, and this might surprise some, but I'm actually NOT against it. I used bots in games myself many times, wow, aion and a few others, I actually really enjoy setting up a bot and usually end up fixed to the screen watching my character do it's stuff - which I know defeats the purpose of botting but I find it kind of mesmerising for some reason lol. Even the few mobile games I play now that have auto-mode I can't help watching.
However, I'm not sure it would be a good idea or not. It would be nice to have for farming, and levelling I guess, but levelling is really slow from killing monsters unless you pop some Monster EXP potions, the way to level here is definitely by doing quests.
Pros
Great for people with limited time to help level up
Great for AFK farming
Increased gold income from selling items and money drops
Cons
More AFK people farming stuff which to other players is just as bad as not seeing any players at all.
The game has limited inventory space - I doubt you would be able to farm for long before filling bags, especially on lower level maps where the mobs have quite a large variation on drops.
I think we had a similar discussion some time ago when somebody suggested it but I'm happy to have the conversation again - see what everyone else thinks about it.