Photoshop CC offers the following enhancements (vs Photoshop CS6):
Support for new cameras (launched after July 2015). As of July 2015, Photoshop CS6 will no longer be updated to support RAW files from new cameras. You can work around this by using Adobe’s free DNG Converter or a 3rd party RAW converter. If you don’t want to use one of the options from Adobe, I would recommend taking a look at Capture One. At $299, you won’t save money for a long time with Capture One, but it offers an extremely good RAW conversion. Or you could pick up DXO Optics Pro for $99.
Camera RAW filter lets you keep adjusting RAW images when opened as smart objects in Photoshop. You can additionally use this tool to make familiar Lightroom/ACR adjustments to any pixel layer (such as to add clarity).
Better support for extension panels (“plug ins”). As a software developer, I can attest that the latest versions of Photoshop offer the ability to create much more beautiful and powerful extensions for Photoshop. As a small example of this, my own Lumenzia luminosity masking panel for Photoshop has an enhanced user interface when running on CC, and offers a few enhanced functions that aren’t possible on CS6. And there are many other extension panels out there from other developers that require CC or later.
Face-Aware Liquify to easily retouch the size and shape of various parts of people’s faces. This is truly an incredible tool if you shoot portraits.
Perspective Warp to fix distortions. This tools is also incredibly useful for landscapes to increase or decrease emphasis on something by making it bigger or smaller within the image. For example, you could make a distant mountain look larger.
Content-Aware Scale: Stretch an image without distorting important elements like people.
Content-Aware Move and Extend with scaling and rotation.
Content-Aware Crop to fill gaps when rotating an image or extending its boundaries (great for adding a little more sky).
Content-Aware Panorama to fill the gaps when stitching images.
Path Blur added to the Blur Gallery. This is an incredible tool for adding motion and energy to an image. I use it frequently to simulate a long exposure effect in my photographs.
Spin Blur added to the Blur Gallery. This is perfect for making making a parked car look like it is in motion by spinning the wheels.
Updated Smart Sharpen adds noise reduction and a better interface.
HiDPI support on Windows. This allows you to make the Photoshop user interface larger so that it is easier to read on high resolution monitors.
Camera Shake Reduction to salvage handheld images that should have been shot on a tripod.
Real-time healing brush. This offers a fast and accurate (live) preview of the healing brush. Note that some users (especially people retouching skin on portraits) may prefer the results of the legacy brush. You can switch to the legacy healing brush by checking Preferences/Tools/Use Legacy Healing Algorithm.
GPU acceleration for certain tasks (healing brush, sharpening, enlarging). Note that many older computers cannot take advantage of these GPU features.
Focus Mask allows you to create a selection based on areas of the image that are in or out of focus. While I love the concept, this tool creates a hard-edged mask for which I have yet to find a use.
CS6 Extended Features (video and 3D, which are not in CS6 Standard).
And the list grows if you’re using a version of Photoshop older than CS6.