Joining a fleet (or guild) has many benefits, depending on your needs. If you wanted to power level your character, fleetmates could help. Better gear and tons of advice also help. But generally yes, this game is essentially played at one level, 50.
Fleets help most by being able to have a competent group to run STFs with, without that, you are at the mercy of random groups (afkers, trolls and ignorance are common in pugs). STFs groups of 5 (sometimes more) which involve transwarping somewhere to shoot the enemy, but most can be run much easier with specific tactics.
The game really begins at level 50, however being in a fleet when your leveling up has a lot of advantages, you can really get contributions up while leveling with the free Doff's you get at Starfleet Academy/Klingon Academy and contribute them to get fleet creds. Fleet Creds allow you to buy shiny fleet items that make your ship quite a spectacular thing to behold lol.
I leveled up to 50 Solo but had tons more fun when i Joined my fleet and I wasn't a sociable person by nature lol but to save your sanity when you do STF's don't pug it fleet it xD
To answer your question, OP: The social aspects are something you get to decide for yourself. As well as how much or how little you want of them. Joining a Fleet is just one way to do this. There are advantages to being in a Fleet, but these are not forced on you. If you're a social person there are lots of people who will be glad to make your acquaintance. Leap without looking first and never look back. If you are not a social person and you like your interpersonal contact strictly regulated then STO is okay with this too.
There is no specific place in the game where it states, "From this point on, it is only groups which are allowed to proceed." There are many things you can do after your toon reaches level 50 which do not require you to participate in groups.
The Fleet I am in is very laid back and doesn't require a great deal out of me. Which is fine because I am not a social animal by nature. I do Fleet STFs when I choose and get left alone if I choose not to do so. I do like finding newer players in game and running missions with them. So they can avoid the boneheaded things I did when I first started playing STO(Skittles Failboat, anyone? lol) The majority of my game time these days is spent earning resources and then contributing them to the ree-donk-u-lously expensive clubhouse known as a Fleet Starbase.
Last pieces of advice before I get off my soapbox.
- Have fun and kill Bad Guys.
- If it ever stops being fun, stop playing.
- Never let yourself forget this is a game, not a lifestyle choice. If you do, stop playing.
- Some of the people you will meet are awesome. Some are tiresome. Only you can decide which is which.
- Play the game the way you want to. Not the way someone else thinks you ought to.
- Wherever there is Ebil, there is also Shiny!
I leveled with a friend of mine and it was great! The feeling of having at your side a captain you know and you can rely on is fantastic. The number of MOBs adjust accordingly and honestly, I think the battles are tougher when I duo with him then when I solo. Yesterday I ran the Tau Dewa patrol alone and it felt easier alone than with my friend. Go figures.
Anyway I'm used to other MMOs where at every corner there's this Elite quest you can do for additional goodies but you don't get that in STO. Hell later on you can even rerun past missions for the same but level-adjusted rewards! So... no. No real group content before 50, besides the random Distress Calls.
Since I'm relatively new to the game (6 months) I also found that as opposed to other MMOs, there is no real danger to cruise around the universe in your starship. I read that once you could get jumped on by the various enemy contacts but not anymore. I thought that was a great idea but yeah, I guess it would bother players more that what it's worth.