High pop server - pros.
Easy to get dungeon grops.
sellers on the auction house make a lot of money.
World feels more ‘alive’ if there are lots of players running around - but perversely this is not always the case, due to THE META. More about THE META later.
High Pop Realms Cons:
THE META rules the hearts and minds of huge sections of the population, especially hardcore progression players, and THE META tends to set the pace of the realm.
Sometimes almost impossible to complete quests, due to having to constantly compete for spawns.
Far greater risk of being ganked and corpse camped.
Massive competition for crafting materials and reagents.
Buyers on the auction house have to pay hundreds, sometimes thousands of gold due to economy hyperinflation.
Far higher number of bots.
Prevalence of ‘booster mentality’ - people levelling by paying others to run them through dungeons for money.
Prevalence of ‘min/max’ mentality. Once again due to THE META.
Prevelance of GDKP. ( a system of raiding and loot allocation where players pay gold for a spot in the raid, or for reserved loot).
Large player populations can make for a less friendly, social or welcoming experience for new players, sometimes increasing toxicity and toxic behaviour.
Guilds far less welcoming, as they have the liberty to pick and choose their members. Those guilds who do advertise are sometimes not very social, and you’ll be there to just ‘make up the numbers’.
Battlegrounds tend to be Horde dominated, once again this is due to THE META.
The Horde have their own problems, in that they have to face longer queue times.
if you choose to raid there’s a good chance you’ll be forced to conform to THE META yourself, else you won’t get a spot.
Low Pop Realms Pros:
More friendly, more sociable. Sometimes a stronger sense of community.
Slower pace of life (some may consider this a con).
Less competition for quest mobs, crafting materials and reagents.
Good for buyers, as auction prices are low, and no hyperinflation.
Far less conformity to THE META, though it does exist in a more limited form, but you have more freedom to play whatever class, build, spec and professions you like.
Dungeon groups more likely to succeed and stick with it, due to difficulty of replacing players who quit.
Raiders more forgiving of mistakes, and more likely to take less experienced, or less well-geared players.
Less ganking.
Far more friendly, casual social and levelling guilds to choose from, eager for new members.
Low Pop Realms: Cons.
Harder to get casual dungeon groups (known as PuGs - Pick Up Groups) due to less players. Shortage of tanks and healers.
World can seem far less alive (though perversely this isn’t always the case, due to THE META).
Less likely to see all the end game content, due to less people generally raiding, and those that do being quite tight-knit.
Terrible for sellers on the auction house, as you’ll get low prices for goods. This makes it far more difficult to get things like epic mounts etc.
Less prestige - the big, famous, super-skilled hardcore guilds all play on the big megaservers, as do the Youtubers and streamers.
Big world PvP battles nowhere near as common.
If you’re curious about THE META (upper case deliberate) which stands for ‘most effective tactics available’, and why many consider it to be a very negative thing in MMOs, then no need for me to ramble any further. Watch this excellent video by Josh Strife Hayes:
The reason THE META can make the world actually less alive, is because it demands that the fastest, most efficient way to level is to be boosted through dungeons by a level 60 rather than do quests; and on high pop realms there are plenty of L60s willing to do this, and charge gold for it. You’ll see ‘boosting services’ advertised (spammed is more accurate) in public chat channels.