We've been studying for our Platform App Builder Transition Exam, and one of the topics listed in the study guide (and in SalesforceBen's helpful post) is Compact Layouts.
In short, according to the Salesforce Help site, "Compact Layouts are used in SF1 and Lightning to display a record's key fields at a glance."
We were already familiar with these to some degree, as we actively use them in our own Salesforce org:
...but in studying further and trying to learn all the details, we got a little confused! Now that we're un-confused, we are here to share our newfound knowledge.
We read the documentation (about 47 times) and noticed something strange, so we asked The Internet:
Compact layouts question -- the 1st 4 show up in SF1, the 1st 5 in Lightning Exp. But why can we add 10? What happens to the rest? #askforce
— Allison Klein (@nyalli) February 22, 2016
All the documentation talks about adding 10 fields to the Compact Layout, but all the explanations of how they get used seemed to only talk about fields 1 through 5.
Turns out we kept missing a key line in all of those help materials, which The Internet helpfully pointed out for us:
@pchittum @nyalli They drive what appears in the feed item when a record is created via publisher action: https://t.co/XKp4Vs0hZB #AskForce
— Rob Alexander (@RobAlexander) February 22, 2016
Right there in the "overview" lesson (and in the release notes), it says "In the full Salesforce site, compact layouts determine which fields appear in the Chatter feed item that appears after a user creates a record with a publisher action."
We're still not sure how we missed that sentence every time we came back to this page! We think it's because the "definition" of these layouts is always described as being about mobile and Lightning, so we weren't expecting the fact that they get used in SF Classic as well; also, we started learning about these from the SF1 Mobile lesson in Trailhead, which doesn't talk about their application in SF classic for obvious reasons.
We tested this and sure enough, it's true:
So! There's the answer to why compact layouts support up to 10 fields!
If you're not using them yet, you totally should! It's the closest thing we have right now to this popular Idea in that it allows you to bring certain fields to the top of a record in SF1 that might not need to be at the top in SF Classic. For example, our Opportunity page layout are huge, and organized into sections that make sense and are helpful when you're using a browser on the desktop, but there are important fields scattered all over the page that we can pull together into a compact layout so they're still visible at a glance on our phones.