"Together or alone" - Sounds like a line from a crappy romance novel (I wouldn't know) but every cyclist has experienced riding alone or with a bunch.
So what are the benefits of riding by yourself or with others? Should we do more of one or the other when we start getting serious about our training? These questions relate equally to road or mountain bike riding. Although they seem different on the outside both disciplines have benefits and drawbacks when riding solo or in a group.
Ride your own ride
One problem with a group is riding at the group's level. That super easy or terribly difficult ride may not be what is best for you and reaching your cycling goals. Riding alone allows you to be more aware of your breathing, heart rate, pace and effort and you are free to alter these variables much more so than in a group. Some groups may push you far outside your current fitness level or alternatively may not provide the hard workout required to increase strength.
Riding can be a meditative experience if approached in a certain way. It might actually be the quietest part of your busy day. I find the metronomic pedal action helps me release thinking pressure and facilitates seeing life from a place outside of the stagnant (and stressful) linearity that we always seem to fall into. Instead of working stuff out, you can let it go and allow inspiration and intuition to take effect.
Confidence in self-sufficiency
When I first started doing longer rides it was always with others. When I began all-day rides on my own I became very conscious of being self-sufficient with food, water, spares and other equipment necessary for a big day out. Riding alone does force upon a cyclist the awareness to pack all the essential gear for riding and in doing so creates a sense of confidence and a "can do" attitude when things go awry.
Choose your own adventure
This is certainly true for road and mountain biking. One of my favourite things about cycling is getting on the bike, rolling down the drive and then deciding in each moment where I will go without any plan or agenda. It can be more difficult than it sounds. Sometimes a quick afternoon jaunt around the 'burbs turns into a three hour adventure in the hills out back. Riding alone you can make those left, right or straight ahead decisions in the moment and really go nuts with it!
Motivation and accountability
There are few things that motivate you on a cold winter morning than knowing your mate is waiting, and shivering, on the corner. It's dreadful to cancel on someone at these times. As much as you don't want to go riding, you did say "yes" last night...letting down a buddy is unconscionable to many of us in this situation.
Riding with friends makes you accountable to something or someone greater than yourself. There is no better motivator.
No other sport functions quite like road cycling where the group operates as a cohesive unit resulting in riding at speeds you would never reach on your own. Want to break a Strava record? You're wasting your time trying it alone! Not only does drafting increase the bunch speed and lower the effort required, but it is a well-known fact that many cyclists ride much faster anyway when out with other riders.
Pushing limits, improving skills
It was said that a benefit of riding alone is controlling the pace - sometimes though you need someone to push it up a gear into a zone you may not be comfortable with. "Stretching the elastic" when done purposefully can really increase your strength and fitness on a bike. It also breaks you out of any habits you pick up training alone and introduces you to other ways of accomplishing similar goals.
There is a vast pool of knowledge available within every riding group on the road or the trails that can only be accessed by joining a bunch of riders.
In the end keeping a balance is the best practice. Always riding alone can become stale and boring and may ultimately lead to giving up. Always needing to ride with others can also lead to non-optimal practices and reliance on others to reach your goals.
Whatever you do, try to be aware of your purpose in doing it - whether it's a solo ride to work, hitting tough intervals or a bunch ride to take it easy and enjoy socialising - decide what you want and go for it!