Using a double opt-in sign-up process for email marketing is a best practice for several reasons:

1. Confirming Intent: Double opt-in ensures that the subscriber genuinely wants to receive emails from you. After the initial sign-up, they receive a confirmation email and must take deliberate action (e.g., clicking a confirmation link) to complete the subscription. This extra step verifies their intent and reduces the likelihood of fake or erroneous sign-ups.
   
2. Improving List Quality: Double opt-in helps maintain a clean and high-quality email list. It reduces the chances of spam bots or people providing fake or mistyped email addresses, as they won’t be able to complete the confirmation step.
   
3. Compliance with Regulations: In many regions, email marketing regulations, such as the CAN-SPAM Act in the United States and the GDPR in Europe, require evidence of explicit consent. Double opt-in provides a clear record of the subscriber’s consent, helping you comply with legal requirements.
   
4. Reducing Spam Complaints: Since subscribers must confirm their subscription, they are less likely to forget or overlook the sign-up process. This reduces the likelihood of them marking your emails as spam, which can negatively impact your sender reputation and deliverability.
   
5. Better Engagement: Subscribers who have actively confirmed their subscription are more likely to engage with your emails. They’ve already taken positive action to connect with your brand, indicating a higher level of interest.
   
6. Fewer Bounces: Double opt-in reduces the chances of sending emails to invalid or mistyped email addresses, leading to fewer hard bounces. This, in turn, helps maintain a good sender reputation.
   
7. Reducing Unsubscribes: Subscribers who double opt-in are more likely to be interested in your content. This can result in lower unsubscribe rates since they are more likely to find your emails relevant.
   
8. Enhancing Trust and Credibility: Double opt-in demonstrates transparency and a commitment to respecting subscribers’ preferences. It can build trust with your audience and contribute to your brand’s credibility.
   
9. Segmentation and Personalisation: With a list of confirmed subscribers, you can be more confident in your segmentation efforts. This allows you to send more targeted and personalized content, which often leads to higher engagement and conversions.
   
10. Better Metrics and Analytics: A list of confirmed subscribers provides more accurate data for analyzing the performance of your email campaigns. You can measure the success of your sign-up forms and identify areas for improvement.

While double opt-in sign-up forms offer many advantages, there may be situations where a single opt-in process is preferred, such as for specific marketing campaigns or when it’s more critical to rapidly grow the email list. However, in most cases, the benefits of double opt-in in terms of list quality, engagement, and compliance make it a recommended approach for email marketing sign-ups.