Specificity and sensitivity

Dear forum

I am trying to answer questions regarding medical screening, and
medical testing.

My biostatistics professor asked the following two questions:

1/Specificity and sensitivity are really important for what kind of
study/test?

2/For what kind of study/test is it important to think about the
Positive Predictive Value (PPV) and Negative Predictive Value (NPV)?

I thought that sens/specificity was the analog of NPV/PPV. I need more
insight.

Can anybody help?

Many thanks for your help.

.