Mechanical filters remove physical particles, such as food, fish poo, or plant bits. Biological filters convert ammonia into nitrites and then into nitrates. Chemical filters remove medications, odors, and other impurities. You need at least mechanical and biological filtration in your filter at all times, while chemical is optional and needs frequent replacing. Mechanical filters such as polyfil can be rinsed and reused until they fall apart, but with polyfil being so cheap I generally just toss and replace it whenever my filter flow starts getting too slow. I find that rinsing it only keeps it flowing well for a week before it's back to a crawl due to how well it filters and holds onto particles.
As far as what to use with the polyfil, it's really up to personal preference. I personally would put half of your containers filled with polyfil and half with bio media (ceramic tubes, bio balls, bio stars, etc), but as long as you have a balance of the media types you can't go wrong.