That question in the title above is a tricky question for almost every beginner who wants to start an online business.
For me, the answer is depends on what type of online business that you want to build in the first place.
If you want to make money online through Google Adsense (PPC) or you want to get commission from affiliate marketing, a decent website (with a paid domain and hosting) will be required.
Why? Because you will have more control over your content and you might have the chance grow your website into a popularly massive website.
When you gain huge success in making money through PPC or affiliate marketing, it’s always safer to have your own website hosted in a paid hosting rather than using free blogging service like blogger.com. Because there are some cases where free blogging platform suddenly deletes some successful blog which has been getting mass traffic and obviously generating quite a lot of money. Believe me, you don’t want to experience it.
But if you just want to sell you own products online, you can always use e-commerce platform or social media to drive sales. It’s enough I think.
Or maybe if you want to try CPA, a website is not always required. I know a friend who only use fb ads to promote his CPA program and he makes quite a lot from it without website.
There are also another success story I read in a forum about an internet marketer who makes tons of money using instagram alone.
So the answer to the question is: it depends on your online business type.
I hope this helps!