When is it good to use forms on my site?
Yes. Forms are very handy to have on sites. The contact form is the most common one you will see and probably the least used by visitors. Most people don't want to fill out a generic form. They would rather email you, call you or visit in person if you have a storefront.
People also are untrusting of giving out their email address to a business without knowing who you are or what you will be doing with their email address. However, a contact form is a good way to add email addresses to your email list if you plan to send out email blasts and/or newsletters. (Keep in mind, you should have their permission to add their email address to your email list.)
One way around this quandary is to offer a form that has more specifics in it pertaining to your business and what the potential clients' needs and questions are. This is also a good way for you to pre-qualify a real customer or get more information from them before you talk.
There are lots of other reasons to use forms than just on the contact page, such as for applications, volunteers for nonprofits, suggestion forms for community groups, adding events for publications, surveys, feedback, social media type involvement, contests and raffles.