I’m used to playing on a medium pop realm but some friends want me to play on their realm which is listed as full.
What are the pros and cons to this?
It depends on what you want.
If you play on a low pop server you’re not going to have to contend as much with other players going after the same quest items as you are, or competing for rare spawns like rare hunter pets or rare mount spawns, but on the downside zones will feel barren, you wont have a good AH economy, and if you happen to need help with a difficult quest you’ll be out of luck. Cross server stuff helps some, but not entirely.
On the flipside a high pop server like my own always feels full. Even if I go back to older zones its not uncommon to see people leveling alts or farming transmogs or whatnot. If I go browsing through the appearances and find a BoE world drop I really want it’s almost guaranteed to be on the AH (though on a RP server like mine many are extremely overpriced). I rarely need to use the group finder on the elite world quests, almost all the time there are others there waiting for it to spawn and help bring it down. If I need help with a difficult quest there is almost always someone around, and many (at least current) zone chats have some lively banter going on (especially Vuldun right now as people scramble to get to exalted before 8.3).
It really depends on what you value from your leveling and questing experience. Cross realms make LFR/LFD not really dependent on server population.
I don’t PVP so I can’t speak to the pros/cons there.
For some reason the realm I play in that says “full” has very little people in the world compared to a medium server. I dont know what the deal is.
Frostmourne Oceanic, is considered a “Full” realm, but I really think it’s on par with a medium - high realm on NA
Unless you are on an RP realm, it won’t make a difference to how many people you see out in the world due to sharding. So, the biggest difference is how robust the economy will be. On lower pop servers, stuff is harder to find to buy, tends to be more expensive, and it’s harder to actually sell stuff.
I personally avoid the very most populated servers (say the top 3-4 for progression) as they seem to attract the most tryhards*, but if serious progression is your goal, those servers will have the most like-minded people.
*I define tryhards as those who think they are the best (but are usually average at best) and think all their failures are due to the people around them holding them back.
Moving my chars to the highest pop serve a few years ago was the best thing I ever did. You need people in an MMO to get things done. On high pop servers pugs do things other server guilds cant.