I've been thinking about this a lot lately and wanted to share my thoughts about it. When you share information on someone else's website, you are promoting that web site. You might think you are promoting your own web site when you post on Instagram or Facebook etc. And you are to some degree, the degree depends on how many people actually see that post.
In my experience when you post something your followers might see it, if they happen to be sitting at the computer when you post it or if they have notifications set to let them know when you post, or if they specifically go to your page and see what you have been up to lately. The average number of people for me that saw my posts on Face Book with over 7,000 followers was (wait for it) 60 people. That is horrible. Over time it would increase a little but hardly at all. So the people who were seeing my posts were people that happened to be following me and happened to be on Face Book at that time.
I used to spend money on advertising to get more views and I found that a lot of people saw things I had for sale and they would like them or comment but it didn't always do what I meant for it to do which is make sales!
BUT my 10 posts a day trying to get sales on someone else's site, gave them an incredible amount of benefit because I was posting on their site and millions of other people are posting on their site and the busier a site is the higher it ranks on search engines. Etsy runs very much on this model and they will keep coming up with changes for people to make and work on their site so that more people are on the site making changes and increasing their rankings on search.
I am only one person and I will never have millions of people posting on my site. I am not even sure I would want that *laugh* but I am on my pages every single day, posting something and that is worth a ton in advertising because every post I make and every item I put up is activity on my page and that will keep my page ranked higher than most due simply to activity.
Just as a FYI, my biggest and best marketing efforts come from Google. I know if I am looking to buy something I jump on a search engine and type in what I am looking for and shop and I find that is what a lot of other people do as well. The majority of sales that come from social media sites are "impulse shoppers" and sometimes those sales turn out to be my worst sales! Unless you are on a site all the time posting and posting and posting, which seems to work fairly well for many people but then again is it really working well or are you just building up someone else's web site traffic instead of your own?
I hope this gives you food for thought and I would love to hear about your experiences and thoughts! If you are inclined please email me