I can tell me about my experience in a Yii-1 project. I used http caching and it was working fine. Page caching was also working as expected. But when I used both together, I used to get blank pages as the page caching was returning a blank page some times.
May be the reason is that when httpcaching is checking about the validity of the browser cache, if the cache is valid, a blank page is given as response and it is stored as page cache. I am not sure if this is the reason.
As a general rule, if there is no changes happening in your page, like a static page, you can use http cache to save bandwidth.