when should you actually put rate limits on APIs, like, whens it time,prob depends on the situation but generally, you

hey folks, ive been thinking about API rate limiting lately. it feels like a good way to protect your service from abuse and ensure fair usage. but when exactly is the right time to introduce it? is it something to put in on day one, or do you wait until you see specific issues like traffic spikes or abuse patterns? what are your thoughts and experiences?