Debug mode

While doing development on a web project, you may need to enable debug mode. You do this explicitly in the web.config file. Set the value of the <compilation> tag in the following way:
<compilation debug="true" targetFramework="X.X.X"> where X.X.X is the .NET framework of your project. For example 4.7.1 or 4.8

While debugging helps during development, it creates some overhead in a production environment. It results in additional symbols loaded for each assembly and the additional processing that needs to be done by the webserver. This is why, we recommend to switch off debugging in the production environment. You do this by setting the debug attribute of the compilation tag to false.

This setting prevents the webserver from talking to attached debuggers, but it does not remove the overhead from your compiled code. To skip the generation of PDB files for all assemblies, you must also build your web application project in release configuration. This compiles your application code without any debug attributes and removes the unwanted overhead.
For more info on build configurations, see Understanding Build Configurations on MSDN.