I see a lot of sites use modals for actions such as posting content (often on social sites). For example, Twitter and Tumblr both use modals, but Facebook does not. What is the benefit of using a modal for this instead of simply designing it in-page.
I have my assumptions, but what like to hear your thoughts.
What is the benefit of using a modal for this instead of simply designing it in-page.
One of the purposes for a modal is to keep a user focused on a task and eliminate any potential distraction. Modals usually cover the entire page and laser focus viewers attention on a content of a modal.
In my experience, modal windows are really good for hiding audio, video, message forms, and lots of other items that would otherwise take up space on your pages.
It is purely a matter of preference though. I would say mock one up with the modals, then mock something up without them and see which is better for your user experience.
Twitter created Bootstrap which has a great modal built into their bootstrap.min.js file and is relatively easy to use if you know HTML, JavaScript or jQuery.
http://getbootstrap.com/javascript/#modals - link to modal examples
Good question!
Modal dialogs are all about focusing the user and removing anything that doesn't have to do with the singular task at hand. On top of that, it allows the user a fairly simple path out of that task without a page refresh.
Taking your Twitter example ...
[ user scrolls through the timeline ]
"Hey, that tweet made me think of something profound!"
[ user hits compose button > modal pops > enters meaningless sentence ]
"Okay, now I have that off my chest."
[ user submits tweet > dropped into timeline at point of exit ]
