Specifically things like instanced 5 man dungeons (like Ragefire Chasm or the Deadmines in WoW) which are explicitly designed to challenge a full party of a certain level range. Notably, not endgame content. I'm sure the answer changes based on different factors (e.g. how good are the rewards? What are the drop rates like? Are similar rewards available elsewhere? How long is the dungeon? Am I late picking the kids up from soccer practice?), but I'm curious what folks' thoughts are. I'm personally sour on the idea, but I understand that my attitude is "the less MMO an MMORPG can be, the happier I am", so MMO designers should probably disregard my opinion.
Supplementary Context: usually about once a year, I get the bug to hop into an MMO. However, I am not a good MMO player. I tend to flit around my gaming library like an ADHD pixie on cocaine, and there's no telling how long my interest will sustain itself. Therefore, any "meta" choice I make is purely by accident, and I don't spare even a moment of thought on "efficiency". In fact, I've often thought of my dalliances in MMOs as digital tourism. By and large, I'm there to craft, read quest dialogs, and poke around in the weird corners of the map for a couple weeks before logging off for another few years. Anytime I've ever done group content (which is, admittedly, not often), I'm desperately trying to keep up while someone nukes everything in the dungeon as they sprint towards the end. I wind up feeling like my lackadaisical approach is probably fucking up someone else's farming loop. Now, I don't think either the sweatlords or I are playing the game "wrong" so to speak, but our priorities are in conflict. Maybe I'm letting people-pleasing anxiety get the best of me, but I feel like the person that cares enough to grind a dungeon reward as fast as possible should get right of way over my happy ass who will intentionally sandbag my way through a dungeon if the vibes are right. Therefore, I tend not to engage with such content, if it's not possible to solo.
This has all come to a head because my current preoccupation is Star Wars The Old Republic. Given this game's much greater emphasis on story and dialog than a typical MMO, I actually feel like there's RP content that I want to see in the dungeons, irrespective of any item reward. To the game's credit, many of these can be done solo by selecting the "story" difficulty option before loading in, but not all of them. I just don't want to be the asshole holding up the party cause I want to watch the 3 minute into cutscene (or whatever) while everyone else is hammering their skip buttons trying to get to the boss.
Not necessarily asking for advice, as the solution seems obvious to me (it's "talk to your fellow players", like it always is), but I thought this might foster some discussion, especially from old heads who might have lived the raid life back in the day, but now have different priorities.

Most of my experience with MMOs nowadays is just a fan server to an old kids MMO ( Toontown ), so my opinion isn't as strong, but I still don't like being forced into working with others unless I choose to.
In the beginning of me playing I nearly got softlocked because I didn't wanna do a forced quest to friend another player ( and I'm pretty sure they have to friend back ). Couldn't really progress without completing it, IIRC. Similar thing applied to a quest where I had to do a quest that required me to play a certain minigame that requires multiple players. Despite that only being an anniversary festival quest for a cosmetic item, I was still a little annoyed.
Though, to get into a more serious MMO experience, back when I played Dofus and Wakfu, despite not getting far on either, I was also a solo player. More of a fan of going into dungeons and quests and battles alone. Just made things easier when I didn't have to coordinate attacks with another player who might push/pull the enemy I was gonna attack away or kill them and ruin my turn, whether accidental or on purpose.