Ask HN: When does my company need its own ASN?

With the recent FB outage, I’ve been reading more about BGP and ASNs. Question: when do I need my own ASN? I see all of the digital giants have their own ASN, but I also see companies like Mailchimp as well have their own ASN. When do I need an ASN for my business? Is it when you want to own a block of IPs?