A rate card is your menu of starting prices: by format, and ideally with notes on what usage is included.
It is not a promise to work for that number on every brief. Rush, exclusivity, raw files, and paid ads change the quote.
Why publish one
Brands filter you faster. You stop inventing a number in the panic of a DM. You can still negotiate.
Keep it dated. A card from two years ago trains them to underpay.