Mostly you may need it for:

1. Preventing SPAM (spammy comments, articles, votes etc.)

2. Preventing email collection (obfuscating could be an option: https://freetools.dev/email-encoder)

3. Clean up server logs (bots creates a lot of lines in server log files)

4. Clean up your Analytics (lot of bots may count as real visitors)

5. Security concerns (not only banks have important data)

6. Avoid automatic registrations (your users list counts too)