"Send to Mobile" when sending private message

i'm wondering if i should check or leave unchecked "send to mobile" when sending a private message, and what exactly sending to mobile does if i make it checked? (does it only send to mobile, or does it send to both mobile and laptop/computer?)

it's an important message to multiple people. basically, if i check "send to mobile", would i risk that it'd be bad for them like they'd have to pay for it, or they'd only get the message on their phone and not on a laptop/computer? if i uncheck "send to mobile", would i risk that they don't get the message at all if they only check their mobile phone messages? what should i do here? thanks

also, if i uncheck it, does that mean that it only sends it to their laptop/computer? (i'd be ok with that)