Difference Between Project.Build.cs and Project.Target.cs

I was hoping that someone could tell me the difference between the build.cs files and the target.cs files. I usually work out of the build.cs files, but with UE4.16 comes the new ReadOnlyTargetRules. When I work with plugins, I usually put my “bForceEnableExceptions = true” here, but can no longer do that. I now have to add it to the Target.cs file and am not sure what the difference even is. This cripples my plugin. If I knew what the difference between the two files are, then it will help me come up with a better solution for future plugins.

Also, on a side question, can I put a target.cs file in my plugin folder, or am I stuck using MyProjects.target.cs?

Tried adding a target.cs file to my plugin, but it caused it to throw UBT build errors.

Any luck figuring this out?