I use MC so much for photos management that I have a PC dedicated just to doing it, a fast machine with huge drive, plus backup drives, plus cloud backup. MC tells me I now have more than 61 thousand images, and I still have many more boxes of family photos to scan. (A separate PC in another room is used to show photos to family and friends.)
The huge value is tagging, which then supports smartviews. I avoid MC's proprietary fields, and only use Keywords, Date and Caption, and (rarely) Description for long explanatory text if it happens to be needed (especially, interesting stuff written on the back of print photos years ago). For Keywords I use the trick of nesting to create pseudo-category-tags such as Person names, photo Places, Events, and various other types of tags, in this format: !Places\CH\Zermatt, !Places\US\CA\San Diego, etc.
I don't use MC's image editing tools, instead have MC's Send To set to open selected images in various external apps I use. But it would be terrific if MC's capabilities can be improved. Also, I run Google Picasa 3.9 in parallel, it can be live with MC and they co-exist. Picasa is terrific for quick adjustments (image straightening is very cool), but it is horrible for tagging (and it messes up MC tags unless they are done a certain way).
As explained by Marko, I easily import into MC all photos from family phones, which auto-upload full quality to Google Photos. Then Google's backup app pulls them onto my PC, where MC imports and I organize. I also load the photos from memory cards of my real cameras, from my scanners, from email, etc. All photos go into MC for management, even those that are not for routine viewing -- photos of important documents, product labels, bad things growing on my dog, other oddities, are simply tagged differently, then stored in different MC folders that slide shows ignore.
I have a family room PC dedicated to running a slide show as screensaver. I don't run MC for a slide show because this PC runs MC for music, I've tried to run two instances, images and music, but it is not a stable situation. Also, MC doesn't (that I know of) let me display Caption or other info in the way I desire -- super-imposed, readable from across the room, in an exact position, font, color. To do this I use an excellent screen saver from UK, ABScreenSavers.com, which allows customized display of image and text (via a CSS file) and photo files used and display order (I like random), and more. The adjacent TV is also connected to the slide-show PC; for a non-TV party I have both PC and TV showing photos, ABScreenSaver sends a different random photo to each screen. It is always a huge party hit, so I've sent many people home with the name of the screen saver. Of course, I'd be very happy if MC could fill this need instead, driving the photo show via smartlists would be "awesome".
The other big need in MC is a way to upload the edited, organized, tagged images to one or many "cloud" photo sites for sharing with family and friends. Google Photos is horrible because it does not respect or use any of the above, it just tries to be robot-stupid "clever". But if there are other suitable photo sharing sites (are there?), allowing MC to connect, sign in, and upload would be wonderful.
To restate the oppoprtunity, the photo/image world is exploding. People are taking more pictures of more things/people/places/activities/food than ever. And the business of scanning old print photos into digital is very big. But all of this soon gets overwhelming and needs organization. Dopey solutions like Google Photos can easily be shown to be a black hole, where important photos get miscategorized or overlooked or lost in space.
On the gear side, today's so-called "phones" are mainly promoted for their camera quality, because people love photos! Even actual cameras are selling strongly, Costco displays pricey (in my store $600 to $2600) DSLR and mirrorless cameras near the store entrance, and they do not carry items that don't sell very well.