IPhone photostream vs camera roll, are they taking up too much space?

I don't understand what is the point of having both. I have 1000 photos in photostream but 988 on camera roll… And they are of the same photos. Can I safely delete one of these albums and still keep all my photos? If so which one do I delete and how can I do it?

When you delete photos on the photostream, it also deletes its copy on the camera roll. But when you delete photos in the camera roll, it will stay on the photostream. But not all photos on my camera roll are on my photostream. Before all my photos consume all my memory space, I transfer them to my laptop and delete them on my phone afterwards so that I can take new pictures. Before you delete some, make sure you back them up first on your computer so that you won't lose precious photos of yours.

Are you sure that the photos are all there twice? More likely they are only there once but you have 2 indexes pointing to the same set of files.