A good website, can help you :
1) Build up your brand and reputation
2) Get new clients and new investors
3) Promote your products and services to the whole world
Can I just use the FREE Social Media such as Facebook, Instagram and Twitter?
Yes you can them. But in real business, using FREE social media alone is bad for your company image. Many people might think you are doing temporary business and not sincere. Because you not willing to invest to get your own website. How can the clients have confident that you are not doing a scam business or "hit and run" biz? It is the "Confident level" and credential that will hurt your business. So you need to have a proper website along with your social media.