Advantages: Huge density of talent, capital, entrepreneurship, potential clients. E.g. there are regular meetups about every niche technology, where you can validate idea/find initial clients. Even if you bootstrap, you indirectly benefit from your clients having VC money.

Disadvantages: Cost are huge, competition on talent is ultra intense. E.g. if you move from Spain, you need to spend incredible energy and time to get through visa pain.

Is it worth it? Depends on your case. IMO bootstrapping, not so much. VC heavy business, likely yes.

Networking.

I've seen lots of competition to US startups never getting anywhere, while the US ones were pitching their stuff day and night, be it at conferences or the nearby Starbucks.