First of all, learning any foreign language produces lots of benefits (both from the psychological and the practical points of view).
Some psychological benefits:
- It boosts your brain power (intelligence, memory, concentration)
- It reduces the risk of developing dementia and Alzheimer
- It improves your ability to multi-task
- It enhances your listening skills
- It broadens your vision of the world
Some practical benefits:
It gives you access to better career choices
It provides you with more opportunities to interact with people that speak that language
It allows you to get access to a wider range of entertainment options (from books and movies, to TV shows and even videogames that are not translated in other languages).
Therefore, in spite of the existence of good machine translators, you decide to learn a foreign language mainly for yourself, to give yourself access to a new world of possibilities, broaden your horizons and benefit from your learning in many ways. Moreover, even if the decision to rely on machine translators has its pros, still it is better if you know the language yourself since it can also happen that you may be unable to use the machine translator under certain circumstances (for example if your device stops working).