Not necessarily, but starting with a feed is a great way to bring in your entire catalog at once. This is the way that I started my catalog and I also set-up rules in Launch to feed the catalog on an ongoing basis. However, to do this you must write all your data (name value pairs for the catalog parameters) to the data layer so Launch can pass it. Everything I needed was already available due to it's SEO value.
If you only set-up the rules to pass data to the mbox and into the catalog you have to wait for each product or article to be loaded on site for the data to pass. If all your content, or all the content you care most about, is regularly used by visitors, then the feed might be overkill for you.