This is often a business decision. Cloudflare's bandwidth is free, and with smart tiered caching my operation serves 6TB a month while only paying out 125gb of AWS egress (with extremely hot files).
Wait can you please elaborate more? I have a site that gets a ton of traffic and my biggest bill is AWS cloudfront bandwidth... how can i reduce this using cloudflare?
Switch out Cloudfront for Cloudflare. Or put it in front of it, if that's what floats your boat.