For the end users, it is only good if it serves a purpose. It's up to the individual to decide what defines purpose.
The value added by it being open source is that someone skilled in Development be it any domain may be able to modify the
program to make it better serve the purpose. Its not just one or 10 people working to develop that project but hundreds and
thousands of more which ultimately makes the service get better and better.
Bugs tend to get found and fixed quickly in open source software, particularly if there is a security aspect to the bugs.
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In short, the answer is YOU GET EVERYTHING FOR FREE! There is not just a single reason that you can benefit by join us. To make things simpler, let us list down some of them below: