When we use mesh topology?

Mesh topology is recommended in scenerios where:

-Redundancy/reliability is highly desirable

-Maximum performance is desirable

-Suited for wireless network like ad-hoc

Not being used commonly because:

-Setup cost is high

-Maintenance for this topology is also difficult

-Not recommended for wired environment

I agree with Muhammad Iqbal answer and I add an other disadvantage :

that is the problem of scalability,

the mesh topology can be used when the connectivity is crucial (eg, nuclear center servers...)