what is iCloud with 200 GB of storage? is it necessary?

For the average user? No

• In many cases for an individual user with a single device, the free 5GB storage is sufficient to store the device backup with a modest number of photos.
• More likely the 50GB plan ($0.99 a month US) is used for individuals with multiple devices using the same Apple Account. This is usually enough to store backups for each device and share a large number of photos in iCloud across those devices.
• Beyond that, the storage amount depends on how much data you want to store in the Files app to be shared across devices. The number of apps and more importantly, how much data those apps store on your device that you want saved in your backup, will have an effect on how much iCloud space you will need.

Hello~ Only you can determine if it’s “necessary “. Click on below…

Introduction to iCloud - Apple Support

Also please remember that you’re addressing other fellow forum members who volunteer here to assist as we can.

~Katana-San~

Artist73 wrote: … Is iCloud GB of storage necessary?

No.

iCloud is designed to synchronize Pictures and Files among several devices, so you can see the same pictures, for instance, on your Mac, on your iPhone, and on your iPad. For this purpose, files and pictures are stored at iCloud.com, and new or changing ones are copied around to keep everybody exactly the same. You can also see your files and download them on any device using a web browser. I have a Mac, an iPhone, and an iPad, and for me, it's really great.

If you don't want synchronization among several devices, then you don't need extra iCloud storage.

iCloud does prove a minimal backup, in case your phone is lost or stolen or run over by a truck. But iCloud copies your mistakes as well as other changes, so it doesn't fix those. So, as for backup, you're better off with a small hard drive.