Running on your own computer have its advantages, as does using CoCalc. Some of the advantages of the download version of SageMath:
- Most modern computers, including laptops, have more computing power than the basic plan offered by CoCalc. For example, you can do computations in parallel, as much as your computer allows.
- You can work offline. Great in many situations where an internet connection is not available or just slow.
- Like other files that are important to you, you can backup your SageMath files with your preferred backup solution. They are usually very small.
- You can install software packages, with specific versions, as you wish on your computer. The download version of SageMath already contains a lot.
In any case, it might be wise to export your work from CoCalc periodically, so you will have a local backup in case CoCalc will change their terms or is accidentally unavailable.