While it is quicker, less expensive and efficient to email an invitation, in my book it is tacky. A wedding is an event, a special occasion, and as such calls for a traditional way of inviting people. We all like to receive that envelope in the mail that tells us the bride and groom thought enough of us to take the time to send us an invitation. The look and feel of the invitation makes the even more real and special.
Electronic save the dates, reminders, links to a bridal website, those are all fine. But take the time and effort to do actual paper invites. They don’t have to be overly fancy or expensive, DIY invitations are fine, but do go through the trouble to show your guests how much you value them by sending an invitation through the mail.