To be a professional photographer, a portfolio site is not a nice-to-have thing, it is a must. In fact, I see that is what differentiate a professional and an amateur photographer. Here are a few reasons
If you really treasure your work, you should look for a perfect medium to present it. In this digital era, we no longer rely on print to spread our work. You need an online portfolio site to demonstrate it. Look at Apple, they build their own Apple Store to showcase their product. You need something similar as an online showcase for your work. If you look at my portfolio site , you can see all my work presented there, in the way that I want to show people.
Instead of relying on social website like Facebook or Pinterest, the advantage of having your own website is that show your taste. You can design your website from scratch, you can control the layout and also how your work is presented. It is like the clothes that you put on everyday. How you design your website show your sense of arts. For my site, I have created a slideshow of pictures showcasing my best work in the front page.
You need to establish yourself as a professional. Instead of relying on just social network site, or free blogging platform, you should have your own domain name, which can help building your own brand. And every time people want to see your work, they should type your domain name, and that will be the official site for your brand. For me, it my domain name will be https://jackvisuals.com which is also my brand name Jack Visuals.
After all of the above, the most important thing after all perhaps is to attract customers. You need to show people that you are a serious, professional photographer. The website helps prove all these. In addition, now you can create a blog, bio, promotion etc so people can find you. Reference my site if you are interested.
So if you are serious about photography, start building a site or hire someone to build one for you, cheers!