Precision - Compared to other techniques, moulding allows you to incorporate more features at very small tolerances.
High Repeatability - Once your mould tool is made, identical products can be made over and over again.
Low Cost Per Part - Other plastic processing techniques may require multiple operations, like polishing, whilst injection moulding can do it all at once.
Fast - Cycle times can be as low as 10 seconds.
Material Choice - There's a vast amount of materials available for plastic injection moulding. A range of more common materials, but also things like antistatic plastic, thermoplastic rubber, etc.
Little Plastic Waste - Part repeatability is very high for injection moulding.
