You can upload and save as many datasets as you like. A project is different.
Datasets are the raw photos you upload, and that GeoNadir then processes into the orthomosaic, Digital Surface Model, and Digital Terrain Model. You can upload an unlimited number of raw photos, and we will process, store, and manage them for free.
A project is where you do analysis of the processed products (orthomosaic, Digital Surface Model, and Digital Terrain Model). You can also share the project with others. You can add as many datasets as you like to a project, but best convention is to have datasets in a project that are all linked to each other in one way or another (e.g. all of one specific area, or reef data etc)
Think of a project like a group (e.g. team, social group, committee) within a society. Each group is made up of individuals, but each individual can be part of many groups at any one time and they can come and go as they like. e.g. you can be part of your local sports group as well as a book club as well as a committee at work.
Datasets are like the individuals and projects are the groups. So a single dataset can be part of one or many different projects. Or none at all.
On the Essentials (free) subscription, you can have one project. On paid plans you can have more projects.