Confirming e-mail box is a good way preventing spam robots. Before we implemented CAPTCHA on our website we used to get over 20 spam e-mails a day and when they find a website form vulnerable, the rates goes up like crazy. If the number of form submissions counts toward Webflow subscription, then you don't want to count spam submissions.
Other great features important to the form submission is website referral information. When someone entered a form (a criteria for goal tracking), we like to know how the visitor found our website. Whether it was direct visitor or referred by another website or search engine. In case of search engine referral, we would like to know what keyword was used.
Web to Lead form. A lot of companies use CRM like Salesforce.com, these days and it is an important feature to have the web form (new lead information) directly entered in the CRM database.They normally supply the code which act upon hitting the submit button.