Severance as in a 'voluntary' payment by employers is a US thing that I don't understand. Do you mind explaining why it gets paid at all?
In the UK, it's common for employers to have contractual obligation to pay a notice period, and for longer term employees they are legally obliged to be firing them on capacity or redundancy grounds - so it is common to pay some severance in order to pay the employee to resign themself and sign some legal paperwork saying it's okay.
I don't get why employers pay extra money "just to be nice" where there isn't some legal reason to do it...?
