Originally Posted by Maximuuus

No one had an experience with a D&D campaign ?
I.E Descent into Arvernus is designed for 4 to 6 players. What are the difference when you DM it for 4 or 6 friends ? Is that only a question of one or two more monsters in encounters ? Something else ?

Right now 5e has 6 years in the making so there are many "Encounter" tables or even Apps that allow you to calculate loot and number of monsters, but usually you do it trom stretch.
In most videogames they usually make tougher enemies by adding more hp and give them more damage, but that´s not usually a thing in TT because the creatures have their stat blocks that you don´t tweak unless it´s necessary. You usually play with the quantity and quality of the enemies.
Yo do not only add more minions to the mix, sometimes you use custom monsters (ie. Something sneaky if they fireball their way through any encounter, damage-resistant golems if they excel at one-hit enemies, etc) or change the terrain ( if they´re a group that has only melee characters you put some snipers or mages in a ridge, add traps, make the enemies don´t use skills your players are inmune to, like sleep against a group of elves or put a swamp in the middle),... You know the party composition and the players and you can change some things so it´s different from what someone would do in a videogame.

I do not know if that´s appliable to a videogame, but in my experience when you have more players (or if the players make an above-average strong group) you can tune the difficulty on the fly. You usually plan in advance but you have the advantage of being able to change things whenever you need to.

But if you want to know if you have to change every encounter and add more enemies or improve the quality of the enemies if you have more players? Yes, and you usually have to tweak things the more players you have. The easier way is to add more enemies to the lot, but there are differences. It´s not the same add two melee grunts or a couple zombies more than add another wizard, a gelatinous cube or mephits.

Of course that´s only possible if you are a human DM he he.