If you're upgrading to.1 on your current handset, there's one new feature you'll want to seriously consider: The ability to show more tiles on the Start screen. Previously available only on those devices with a 1080p "Full HD" screen, this denser, more usable Start screen layout is now available on all handsets that can run Windows Phone 8.1, from the affordable Lumia 520 to the flagship Lumia 1020.
Note: If you're already using a 1080p-based Windows Phone 8 handset, like the Nokia Lumia 1520 or Icon, you already have this denser Start screen layout. And no, there's no way to "show fewer tiles" on such devices. This option only appears on devices with screens that have a lower resolution.
Remember, anyone with a Windows Phone 8 handset that has been upgraded to at least Update 2 can get the final, RTM version of Windows Phone 8.1 starting today. Just follow the instructions in my article Get Windows Phone 8.1 as Soon as Possible. Then, get that update going and, while you wait, check out my Windows Phone 8.1 Review and get excited about some of the new features. Here's one you won't find in the review.
If you're using a Windows Phone 8 handset that does not have a 1080p (or "Full HD," or 1920 x 1080) display—that is, any Windows Phone 8 handset other than the Lumia 1520 or Icon, plus a few others—you will see a unique new option in Settings, Start + Theme: Show More Tiles.
When this option is not enabled, you can display a maximum of four small tiles on any row of the Start screen. For example:
But when you enable Show More Tiles, you can display 6 small tiles on any Start screen row. Humorously, when you do enable this feature, the display looks pretty funny, with your existing layout retained but shoved up against the left of the screen.
From here, you can of course change the layout—and tile sizes—as you see fit. And you can create a far more customized display than was previously possible.