There is no limit to how many collections can be created, and they in no way add to the overall storage of your library because they are essentially digital albums made up of "pointers" to images that have been gathered from various projects in your library.
There are many use cases for collections. For example, they can be used in the following scenarios:
Collections behave very similarly to Projects in many respects. Images can be edited and Messengers can be sent from them. Even though they do not hold copies of files, the storage of the images can be managed from Files Perspective; so, images from various Projects put together in the collection can be moved in and out of Cold Storage. And, just like Projects, Collections can be placed into folders.
- A photographer can make a new collection of photos from his/her library every time their personal website needs to be revamped with brand-new portfolio images.
- A stock company's sales representative can make a new collection of related images by theme every time they want to pitch a new story idea to a magazine.
- A television show's photo producer may want to make a collection of all the best single shots of the principal actor in the show for social media campaigns.
Visually, the way to distinguish Projects from Collections is by the shape of their key frame. Projects are square, while Collections are round.