I started using SageMathCloud a couple years ago while taking courses from edX and Coursera in physics and data science. I liked it enough that I joined the project as volunteer contributor. At 60+ MOOCs completed, I still use SMC for online learning. Most valuable features to me: 1) not having to install tons of software locally; 2) consolidation of work from different courses & schools; 3) Sage units of measurement and symbolic expressions (good for physics); 4) Jupyter notebooks and sage worksheets, so work from a study session reads like a lab notebook rather than a jumble of scratch paper notes.