Avantages
One can hide out for years within Orange doing nothing before getting made redundant (as almost no one is ever sacked). If you are a low level employee, it might be okay until you are made redundant. If you are senior employee, please consider your career direction carefully before joining.
Inconvénients
In France, the company has a hundred thousand extra employees which they do not know what to do with. The company cannot fire them due to government restrictions, Orange just tries to keep employees busy with massively overstaffed projects (which usually fail) hoping the employees will get bored and leave on their own, or possibly, commit suicide. Outside of France where the company also has operations, this mindset creates a cancerous mindset in how the company behaves and manages its actions, all to protect its employees in France. Nothing ever changes in Orange, only a continuation of its long term death spiral. If you have a hope to progress in Orange, unless you are French and went to the correct school, forget about it. If you want a pay raise after of few years... forget about it, unless you go ahead and resign, in which case the HR department will panic and give you whatever you ask for.