Mostly relevant if your phone is lost or stolen, or perhaps even if criminals are directly threatening you. For example, I worry about bank accounts when I travel to some countries because criminals would be highly motivated to steal from me - the only thing protecting me is their ignorance. In some countries a few thousand dollars is a lot of motivation. Unfortunately my primary bank does not provide secure 2FA but only provides phone auth, and I am locked into my bank because of my mortgage (I have a mortgage, and conditions have changed which prevent me from getting a different mortgage from another bank). I could cancel revolving credit (the main financial risk) but that has other opportunity costs for me.

Also SIMless helps prevent unwanted telephone charges - important if roaming in other countries on account. Phone companies do not make it easy to limit your liability, so if you are unlucky you could end up owing many thousands.