Whyzer can research an account perfectly well without knowing anything about you, but the output will be generic. Adding your product is what turns "here is what this company is dealing with" into "here is why what you sell matters to them."
What to write
Go to Products and describe what you sell the way you'd describe it to a colleague, not the way it appears on your website. What problem it solves, who typically buys it, what it replaces, and what a good-fit account looks like. Positioning language beats feature lists here, because the model is using this to draw connections to the account's situation.
If you sell more than one thing, add them separately. You pick the active product when you generate a dossier, and the same account can produce very different points of view depending on which one you're selling.
When to revisit it
Whenever your positioning shifts. New messaging, a new segment, a repositioned product: update it here and every dossier you generate afterward will reflect it. Existing dossiers keep the positioning they were generated with.
On a team, products can be shared so everyone sells the same story.