Frames are used by many webmasters to have a main page and then several secondary pages in it.
It makes it easier for them to just design the navigation one time instead of having to do it on every single page. Sounds nice, right? It’s not!
For one, you can’t link to specific pages, as all of those are acessed through the main page and there is only one link: the one on the main page.
This is also bad for search engine optimization. You want search engines to find that content, but with frames it makes it harder for them to do so.
Another thing is keeping it fresh. Give users reasons to come back with quality, fresh content! If they keep coming back, it’s more likely they’ll buy your products.