It seems like the purpose of Vagrant is to easily and consistently create VM environment: either multiple VMs for testing, or sharing the same VM setup with others. (based on what I read, no experience here)
Is there a particular use-case for Vagrant where
i) I already setup my VM environment
ii) Not much sharing or duplication of the VM environment is necessary
iii) I actually code within the VM, not just as production/testing environment
The strongest use-case for Vagrant is to set up separate VMs for each project. This allows you to ensure a clean, stable environment for each project you may have, without it being cluttered by dependencies from other projects.
Is there a particular use-case for Vagrant where i) I already setup my VM environment ii) Not much sharing or duplication of the VM environment is necessary iii) I actually code within the VM, not just as production/testing environment