What exactly "Assignable" for Roles works?

Summary:

Hello team,

I need to understand what "Assignable" works exactly?

Navigation: Tools>Security Console>Users>Search any user>Click the same>"Assignable" is visible.

Sometimes "Assignable" is YES to the roles and for some roles, it is NO.

Can anyone help me to understand the same, how it works?

If any test case be shared, then it will be really helpful to understand.

Thanks in advance,

Latika

Content (required):

Hello team,

I need to understand what "Assignable" works exactly?

Navigation: Tools>Security Console>Users>Search any user>Click the same>"Assignable" is visible.

Sometimes "Assignable" is YES to the roles and for some roles, it is NO.