Vendoring gems solves lots of problems: GitHub/RubyGems outages, yanked gems, credentials sharing in CI/CD, and as a bonus, deployments are quicker.
Negative side effects: You need to update your vendor cache periodically, your repo increases in size, and native gems have problems if if you develop on a different platform than you deploy.
Negative side effects: You need to update your vendor cache periodically, your repo increases in size, and native gems have problems if if you develop on a different platform than you deploy.