When sending parameters from C# to SQL Server, instead of .AddWithValue():

string SomeString = "some string";
...
cmdObject.Parameters.AddWithValue("@StringParam", SomeString);

Most rightly suggest .Add() instead (e.g. "Steve" in this Stack Overflow answer):

string SomeString = "some string";
...
cmdObject.Parameters.Add(new SqlParameter
{
    ParameterName = "@StringParam",
    Value         = SomeString,
    SqlDbType     = SqlDbType.VarChar,
    Size          = 255 // given the column is varchar(255) (-1 for max)
});

Why? It allows you to be more explicit about the type being passed in, as well as the length, and has other performance benefits as well.

• Bob Beauchemin talks about multiple ways AddWithValue hurts performance:
  Under the Table – How Data Access Code Affects Database Performance

• Erik Darling explains the impact of parameter sizes in this answer:
  Parameterized query creating many plans

• Dan Guzman also talks about the performance issues:
  AddWithValue is Evil

• And Joel Coehoorn has been begging us all to stop using this method for years:
  Can we stop using AddWithValue() already?