There are several technical differences between these two types of requests, regarding length limitation, security, caching and a few others. But if someone asks you WHEN would you use it, I'd say one of the most important points that any front-end developer should take into account is that we should only use GET for idempotent requests, it means requests that don't make significant changes in the backend system or database but if you do need to make inserts, updates or deletes in a database, trigger emails or any other major action, POST is recommended.