It depends on which app you are using to store photos in the cloud. iCloud Photos still takes up storage on your device because you cannot upload photos to iCloud and then delete them off of your device. All that iCloud photos does is give you access to all of your photos on all devices and it keeps whatever you do on one device in sync across all devices. So that means if you delete a photo on your iPad, it would be deleted on your iPhone, your computer and in iCloud itself. Using iCloud photos will help save some space on your device when you optimize storage.
This explains how to set up and use iCloud Photos.
Set up and use iCloud Photos - Apple Support
Should you decide to use iCloud Photos you may need more storage than the free 5GB of space that Apple gives you. It’s fairly inexpensive when you consider that you can get 50GB of storage for 99¢ per month. The way if works is that you pay that 99¢ charge every month for a total of 50GB of space. You don’t get an additional 50GB every month, you get a total of 50GB to use.
If you are interested in more iCloud storage, take a look at this.
Buy more iCloud storage - Apple Support
The pros to using iCloud storage is that you will save some space on your device. How much space spends on how big your photos library already is. The downside to it is that it is not real off device storage. You can’t upload photos to iCloud, store them there, delete them from your phone and download that again when you want to view them again.
You may want to look into other cloud solutions, like Google Photos or DropBox. There are other apps that you can use as well, but I’m not real familiar with any of them because I don’t use them.
