Real life obligations from my players make it so despite the fact that pretty much every week there's a game of D&D that I run at my place, not every player can show up all the time. That has many consequences on my campaign, both good and bad. In no particular order, and mixing the good and the bad, here are the consequences I have noticed:
- Because not every player can show up every week, everyone has to stay at the same place for the characters to be able to meet up when it's game time. We can't leave a game to be continued in the middle of a forest if we're not 100% sure that the very same exact group of characters will be back next week, we have to bring them back to the status quo setting of the city.
- I have to use dungeons sparingly since they have to be within or at least very close to the city, even for a Fantasy setting it would be silly if they showed up too often in such a small area of the map. The sewers and natural caverns nearby are my dungeon replacements so to speak.
- Every game has to have a clear 'end of the game session' moment. We can't pick up exactly where we left off next time. Sometimes it means rushing the end a bit or asking the players to sort of collaborate so the story can stop at a specific moment.
- Cliffhangers are difficult to manage, it's important to have players who will sort of metagame (normally a dirty word, I know) in favor of the reality of how the game is managed. Characters will not look for their colleague if the player of said colleague is not present that night. Kind of reminds me of superhero comics where in their solo titles they never call for help from their allies but in the group titles they're quick to do so.
- Characters get to know the city well and its ongoing storylines so they get attached to the setting and situations naturally without much effort from the DM. They also make assumptions about what's really going on behind some plots. They can be eerily accurate or amusingly off the mark, sometimes in a single session.
- Prep time is extremely easy when you don't have to create everything from scratch but have instead an established setting that you know well. Often you don't prepare a specific series of events as much as you decide what every NPC will want to do and just play it out logically.
- It's difficult to make it all seem new and fresh after a while, so you have to shake things up a little bit when the players start getting too comfortable.
- In a game where character death is something that can totally happen, players will often have to remind themselves that secrets that previous characters have uncovered are not known by their new characters. In a game of exploration that moves from one place to the other it's easier to remember than when the players really get familiar with one specific place.