When should you use flexbox?

Question

HTML

Are there any restrictions on the use of this technology? Indications?
Or should it always be used?

Answer 1

Or should it always be used?

at the moment (as of February 2017) "always" it is not worth using it yet.
use it for those purposes when without it you would have to fence crutches.

Answer 2

Are there any restrictions on the use of this technology?

Support for older browsers.
Where to lay out elements with flexbox, with line-length expansion, and other things that are hard to do without it.

Answer 3

You should not use it for layout, because. Safari still has a lot of bugs when using flex.
And so, in principle, there are no restrictions.