Social media, as you probably know by now, has become one of the main sources of news and means of communication for most people. This means that these platforms are used by billions and billions of people.
You cannot afford to neglect your social followings for this exact reason.
That and it's also a form of social proof. People will tend to follow those who others follow. Labels will look at your following when they decide about working with you. The same goes for collaborators, bloggers, press and influencers.
Now, you don't have to be on every social media platform. If you know your potential tribe likes to use a certain platform it's a good idea to be there. I'd say start with 3 platforms. Instagram, Facebook and Twitter for example.
Keep in mind however that the more saturated a social media network becomes the less attention you'll get for free and the more attention will start to cost. So, while it may have been easier to grow a following on Insta when it started it will get progressively more difficult to do so as the platform grows.
So, it's a good thing to stay updated on newer platforms that are starting to get traction for better organic traffic and attention.
There may also be opportunities when these platforms release new features as long as you're an early adopter of the feature. Take Instagram's longer-form video feature, IGTV, for example. When the platform releases new features they often reward those who use it first with cheaper attention and more traffic.
Another thing to remember is that each platform has a type or format of content that works on that platform. So, what works on Facebook won't be what works on Instagram. This means it's a good idea to make your content tailored to the platform you're posting on.
Keep in mind though that you'll not be able to reach most of your social followers organically. Facebook, for example will only show your posts to some of your followers. To reach more of them you'll need to pay...