Why is this an issue?

Unnecessary keywords simply clutter the code and should be removed. Specifically:

• partial on type declarations that are completely defined in one place
• sealed on members of sealed classes
• unsafe method or block inside construct already marked with unsafe, or when there are no unsafe constructs in the block
• checked and unchecked blocks with no integral-type arithmetic operations

Noncompliant code example

public partial class MyClass // Noncompliant
{
  public virtual void Method()
  {
  }
}

public sealed class MyOtherClass : MyClass
{
  public sealed override void Method() // Noncompliant
  {
  }
}

Compliant solution

public class MyClass
{
  public virtual void Method()
  {
  }
}

public sealed class MyOtherClass : MyClass
{
  public override void Method()
  {
  }
}