I think it’s standard practice, as a project grows, to migrate it to more stable and scalable platforms. I have several projects on hostpro.com; some of them were originally hosted on shared hosting, but as my online store grew, for example, I realized that the site needed more resources. Once I decided on a plan, technical support helped me with the migration.
I based my decision on the site’s statistics and traffic levels. A good hosting provider tracks resource usage, and if you consistently hit your limits, that’s a good reason to consider switching to a VPS.