For the life of me I can't find the link right now, but it was from Pat and Bingo Card Creator. He requires an account for troubleshooting and support purposes. The vast majority of support is from first time/free users and when they did not create an account, support was a headache at best and impossible at worst. Perhaps there were other solutions for him, but if you can get people to create an account and it makes your life easier, why not?
A/B testing could determine whether my hypothesis is correct, which is: more people will use and share a site if an account is not required to use its minimal functionality (think pastebin, jsfiddle, and Wikipedia) because account creation is a barrier to usage.
Thought-experiment. Imagine two nearly identical websites: one requires registration and the other does not. What site will people be more likely to use?
There were other solutions to the troubleshooting problem. For example, only registered accounts can contact for support. Note that there are three types of accounts: an unregistered account (free), a registered account (also free), and a premium account (paid).
Sure, but one really has to ask themselves whether it's worth that trouble.
I'm certainly not saying you are wrong, but looking at a product like Bingo Card Creator -- something that's really only worth keeping up if the work is minimal and the profit's fairly steady -- I doubt I'd go to the trouble.
And as someone who works for a public service institution, the "only registered accounts can contact support" is a nice sentiment, but rarely works in practice. What ends up happening is that people didn't read that particular piece of fine print and now their pissed that you won't help them and you'll never make that conversion to a paid account. Obviously Pat tried it your way and made the determination that it would be better for his product’s future to limit engagement.
You're working on the assumption that engagement and conversion of the maximum number of people is the sole goal. Perhaps there are other considerations that creator has.
It's nice to work from first principles, but once the product is on the ground, you really have to revisit your own goals for the product to make a determination what will work best.
