Everyone is different in terms of what they can/not tolerate in another person.  A roommate search (ideally followed by a roommate experience) is a good way to figure that out, possibly as a lower-investment form of "training wheels" or a refresher course for more important relationships.  If you can't learn to make it work with a more casual roommate relationship, you're pretty much doomed to mess it up when living with a long-term significant other partner . . .  or doomed to start your next roommate search sooner than you'd probably like.

Personal Security – Living alone can be scary at times, especially in a new place.  It feels (and probably is) safer to have other friendly humans around your home.

Emotional support and safety – A roommate can be nearby in a crisis, and/or someone to be home with your stuff at least part of the time that you're away.

Financial – Not paying rent/mortgage and utilities on an entire dwelling all by oneself is an easy and quick way to save money, either for other financial priorities (starving artist/student, anyone?), to afford more of the finer things in life, or to save up for your own place/your own mortgage for the future.  That is, if your roommate search turns up the RIGHT roommate.  You will need to find a roommate that's compatible with you and your lifestyle, long enough to stay for a good chunk of time.  Otherwise, the multiple deposits you'll have to pay for new roommate situations will put a serious dent into the money you'd otherwise be saving.

Social life enrichment – If you find the right roommate some of their friends may become yours and vice versa.

More space for less money. - Even though you'll be sharing it, living spaces with multiple bedrooms also tend to have larger living rooms, kitchens, etc.  If you ever experience claustrophobia, this can't help but be an improvement over a studio-type situation . . . as long as you get along with your roommate.

Expand your mind – A roommate search leading to multiple interviews and an experience with a roommate that's not exactly like you, your family, or the close friends you have already will teach you important life lessons about, you know, diversity and people and stuff.

Cut back on the tasks involved with moving to a new city, or moving away from your family for the first time – Moving into an already established household will drastically cut back on the number of chores you'll need to accomplish.  There will already be electricity, probably a sofa, maybe some spoons and forks you can borrow, etc.

"Test-driving" your more general social skills . . . learning how others react to you up close and personal – When feeling offended by something, is this something most people would find not terribly offensive and I should just get the hell over it, or is it just me?  Am I self-absorbed, or lacking in self-esteem? What should be tolerated vs. what is totally inconsiderate?  As baby fledgling adults . . . or even adults re-entering a social market, most of us need some practice or reality-testing here at some point.  An intelligent roommate search will provide you with just that.