Since you're inviting us to suggest why it is useful --- I come from using Dropbox, Google Drive, and then OneDrive for years and years. I settled on iCloud cuz it works well with my Apple Devices. I have a family and together we're all using 330GB of data - so I pay for the 2TB plan anyway so that my wife, her mother, and I can have iCloud Storage to backup all of our Apple devices to, store all of our photos, and house all of our data. It's super convenient when it comes to iMessages, backups, photos, and data.
IMO iCloud Backups are far superior to iTunes backups because - time saved. Having my photos instantly backup to iCloud is worth it - especially when I'm out and about taking photos I want saved the instant I take them. Same applies to my wife and my mother in law.
With iCloud Photos optimized storage - I can have access to all of my 53,000 photos and videos - while only taking up 9GB of space on my iPhone - I take a photo and it is instantly accessible on my iPad and MacBook.
My wife is doing her PhD and stores all her data in iCloud - so I moved my 150GB of data to iCloud and it has been pretty good. I still use OneDrive for work and my PC but iCloud on my personal PC works amazingly well (syncs my latest photos there too).