Not every visitor is ready to buy or sign up. This section's job is to not lose them entirely — capture just an email so there's a channel to reach them later. Keep it to one field and one button, as light as it can be.
Feedback matters: the instant someone submits, the form should switch to a success state (a checkmark, "You're subscribed") — leaving the form as-is makes visitors unsure whether it worked, so they either resubmit or leave. Stating what they'll get and how often ("one email a week, product news only") in a single line lowers the barrier to signing up.
Asking for a password or a full name alongside the email makes a newsletter signup feel heavier than it should, and drop-off climbs. And sending anything other than what was promised — sales pitches instead of the newsletter — breaks the trust that got the email in the first place.
When to use
Fits content or blog-style pages where most visitors won't convert on the first visit. If a strong CTA (like a free trial) already exists, don't place a weaker email-only CTA next to it — they compete.