what is the benefit of adding UserClaims 'role' to IdentityResource - identityserver4

Question

why we add , or what the benefit of adding UserClaims 'role' to IdentityResource
new IdentityResource { Name = "role", UserClaims = new List<string> {"role"} }
it's not add the roles to the token
i can only add the roles to token by adding UserClaims 'role' to ApiResource
when i remove UserClaims 'role' from IdentityResource my project also work fine.

Answer 1

The 'UserClaims' that are identified would be required for a user to have in their identity token when they try to use the particular resource.
If this resource was an API and you had the UserClaim 'Admin' defined.
new IdentityResource {
Name = "MyAPI", UserClaims = new List<string> {"Admin"}
}
The API methods would not be able to be used unless the user had the 'Admin' claim.
IdentityServer4 Documentation.
UPDATE:
JwtClaimTypes.Role is a common claim type or group. I don't think it would be common to have a claim value of 'role' in the claims type of JwtClaimTypes.Role.
See the following example: (Source)
var claims = principal.Claims.ToList();
claims = claims.Where(claim => context.RequestedClaimTypes.Contains(claim.Type)).ToList();
claims.Add(new Claim(JwtClaimTypes.GivenName, user.UserName));
//new Claim(JwtClaimTypes.Role, "admin"),
//new Claim(JwtClaimTypes.Role, "dataEventRecords.admin"),
//new Claim(JwtClaimTypes.Role, "dataEventRecords.user"),
//new Claim(JwtClaimTypes.Role, "dataEventRecords"),
//new Claim(JwtClaimTypes.Role, "securedFiles.user"),
//new Claim(JwtClaimTypes.Role, "securedFiles.admin"),
//new Claim(JwtClaimTypes.Role, "securedFiles")
if (user.IsAdmin)
{
claims.Add(new Claim(JwtClaimTypes.Role, "admin"));
}
else
{
claims.Add(new Claim(JwtClaimTypes.Role, "user"));
}
if (user.DataEventRecordsRole == "dataEventRecords.admin")
{
claims.Add(new Claim(JwtClaimTypes.Role, "dataEventRecords.admin"));
claims.Add(new Claim(JwtClaimTypes.Role, "dataEventRecords.user"));
claims.Add(new Claim(JwtClaimTypes.Role, "dataEventRecords"));
claims.Add(new Claim(JwtClaimTypes.Scope, "dataEventRecords"));
}
else
{
claims.Add(new Claim(JwtClaimTypes.Role, "dataEventRecords.user"));
claims.Add(new Claim(JwtClaimTypes.Role, "dataEventRecords"));
claims.Add(new Claim(JwtClaimTypes.Scope, "dataEventRecords"));
}