I use "page" for anything that is fairly static or not time sensitive like service pages. Pages typically will go in your navigation bar whereas posts usually will not.
I use posts to provide details about the pages. For example, if I had a dentist as a client, I would put teeth whitening, dental implants, wisdom teeth extraction, and invisalign as service pages with general details and benefits of each procedure. I would then write blog article explaining highly specific details about the procedure, answering FAQs, etc.
One benefit of blog posts is being able to use categories/tags as they help aggregate common articles together. Back to the dentist example, frequently, the category or tag pages would rank better than the "services" page because there were 5-6 articles about the topic. \