Dynamic outgoing IP addresses
Because Render only uses the same three outgoing IP addresses, my services get rate limit fairly often when using unauthenticated APIs. One in particular I'm constantly being rate limited at is Discord. On average my service makes 3 or 4 API calls a day to post to a webhook (which is far below their unauthenticated rate limit), but it often fails as the IP address has been rate limited.
There are alternative solutions of course, but I didn't have this issue when I used to be on Heroku as their outgoing IP addresses are dynamic and rotate every so often.