The real use of Pinterest is that each image is associated with its website of origin. So if you are the type of person that remembers things visually, you can use the pins or individual images as reminders of the content of the original websites. It is also possible to do “research” on Pinterest on a given topic. If you search for a particular topic, the results will show all of the pins relating to that topic. Each of the images is really a link to the website where the image originated, so by clicking on the images you can effectively go directly to that website. In this way, Pinterest becomes just another way of organizing and finding content on the Internet.
If you need a place to store genealogically related websites you encounter on the Internet, you can pin an image from the site and then you will have a visual reminder of the site on your Pinterest board. This may ultimately be more useful for finding content, especially if you are a person who thinks visually. Also, if you run across a photo of family members on the Internet, you can pin the image and not only capture the image, but also a link to the website where you found the image.
From that I would conclude that Pinterest is a kind of visual blog, in the original sense of blog, as a web log, a place where you make a list of web sites you have visited and would like to have a record of so you can visit them again.
I have a blog that I use mainly for that original blogging purpose, Simple Links, and I find it quicker and easier to use than Pinterest.
I have several other blogs, which I use for different purposes rather than as simple web logs -- a couple for observations on the world around me, ideas I want to share and discuss with friends, and also genealogy and family history, where I write up some of our research and discoveries for other family members to read.
I have two family history blogs. There is this one, which, like the Simple Links one, does more or less fulfil the original purpose of a web log -- it is mainly links to web sites that I find interesting or useful for genealogical and historical research, like this article, for example. I publicise this blog a bit more than the Simple Links one because I think that some of the links that interest me may be of interest to other genealogists too.
The second blog, Hayes and Greene Family History, is mainly a sort of research log, recording things we have found and problems we have encountered in the course of our family history research. They are things we like to share with other people, because other family members may be interested in research findings, and others may be able to help with some of the queries. But none of these things seems to be served very well by Pinterest. If I want a log of web sites visited that I may want to visit again, I find my Simple Links blog works better. If it is specifically genealogy web sites I want to record, then I use this blog. But I find Pinterest rather confusing and more complicated to use. Other people's minds may work in that way, but mine doesn't seem to, so I look at Pinterest maybe about once in three months, if that.
If I want a visual record of a web page with some of its content, including pictures, with a link back to the original; site, I find Evernote much better. That still works even if the original web site has disappeared -- you can clip whole artlcles, or even pages, to Evernote.
But if you want to know what Pinterest is supposed to do, this article is pretty good.