2. Less often, I use it if there's a trial that catches my eye but I don't want to give them my actual info. I use a single use card in this case.

3. On perhaps less reputable sites where I certainly don't want to give my info. Again, I use a single use card in this case.

4. I use it across all my subscriptions because I can easily see how much I'm spending in a given month (specific to subscriptions).

The cap and single use is the one of their best features; you can assign it any value you want and if it hits that, it won't allow other transactions.

While I'm not familiar with it, I've heard that Citi cards also have the same Virtual Accounts, so you could use that as well.