Is a good practice import namespaces in C++? [duplicate]

This question already has an answer here:

• Why is “using namespace std” considered bad practice? 35 answers
• Is using namespace..like bad? [duplicate] 7 answers

I was reading a friend project in C++ and he doesn't import namespaces in the project. I asked why and he said that it isn't a good pratice, but dont know why. I know about import STD isn't a good pratice, but it's for all namespaces?

Is it a good practice? Why?