Implications of Using Insecure in the .NET Library

Question

I am considering optimizing certain areas in my library (Npgsql, the PostgreSQL driver for .NET) with unsafe operations.

Now in different places it is clearly indicated (for example ) that unsafe code is executed only in a complete trust environment. I wonder what exactly this means in 2016, for a library that is designed to be used in as many contexts as possible - does IIS allow libraries with unsafe code? Are there other environments that do not allow them? CAS and the average level of trust seem outdated, and in general it is difficult to get a clear picture of the current situation.