Why Free Plans Don’t Work
I think you should use a free plan if actively using the 'free' plan will eventually force the user to go to a paid plan. e.g. dropbox.If you just give your core product away for free then users will only switch if they need the extra features of the paid plan. You can still use 'free' for marketing, because total conversion rates with a free plan will probably be higher, just don't expect these 'free' customers to switch if they don't have to.