At TALK, we strive for a sales free environment, only allowing in-house TA/HR professionals to join. Verifying professional emails (issued by your company) during the application process allows for us to ensure that vendors, agencies, and consultants do not infiltrate the group to try and sell our membership. This way, members can be worry free in knowing that they are among peers as they connect, collaborate, and share best practice.
However, in these mobile times, people are just as mobile. Careers are fluid, and people tend to change jobs every so often. This means a professional email addresses are not permanent. We'd hate to lose touch with our members just because they've moved jobs. So, we collect personal emails (Gmails, Yahoos, etc.), to make sure you're always kept up to date about events and discussion on the platform.