What are some success stories of using BPF? What is a scenario where I would want to use this tool?

Cloudflare uses XDP for a variety of things: https://blog.cloudflare.com/xdpcap/ https://blog.cloudflare.com/l4drop-xdp-ebpf-based-ddos-mitig...

Performance engineering, debugging, etc: https://github.com/iovisor/bcc https://github.com/iovisor/bpftrace

Brendan Gregg is all on board the BPF train as well - check out all the blogs he's written about it over the past several years: http://www.brendangregg.com/blog/

IMO, (E)BPF is one of the most exciting technologies to be introduced in the past half decade or so. bcc and now bpftrace have become two of my favorite tools to reach for when assisting EC2 customers with performance issues. (Edit: I suppose I should note that that's a personal preference and not AWS policy, and also that the performance issues aren't special to EC2 ;))