It's not just not needed for small projects it is actively harmful. It's also actively unhelpful for large projects which have relatively more simple logic but

It's not just not needed for small projects it is actively harmful. It's also actively unhelpful for large projects which have relatively more simple logic but complex interfaces with other services (usually databases). DI multiplies the amount of code you need - a high cost for which there must be a benefit. It only pays off in proportion to the ratio of complexity of domain logic to integration logic. Once you have have enough experience on a variety of different projects you should hopefully start to pick up on the trade offs inherent in using it to see when it is a good idea and when it has a net negative cost.