There is a whole world of difference. Figma's servers can be down when you need it to work, developers might want to 'phase out' the function you need, or introduce some changes that would totally break your workflow, and you will be absolutely powerless to do anything about it but conform.
With locally running app you control when and where the app works, and you have way more options when developer introduces some changes that don't fit you.
Meh. I can't open any of our old sketch files at work because I don't have a valid license for a version that works on the newest OS. All the same as being locked out of a server in the moment.
This does not make any sense, newer versions of Sketch open old files just fine, and licences are valid for any version.
Maybe you were trying to say that you can't open new sketch files because your version of macOS doesn't support latest versions of Sketch? That is, indeed, a problem. However, if you work only with internal files, you can simply abstain from upgrading to new version and keep working on the version that works for you. Moreover, Sketch licences do not 'expire', you simply can't receive updates any longer. So you can still work with your files as long as you need, not relying on someone else's actions.
Not to mention sensitive design documents that must stay on-prem can't be uploaded to cloud services like Figma (I don't know if this is possible to do in Figma somehow? I've never looked into it)
