is it necessary or useful to have a safeword with an online only dom?

i may have just found my first online dom, but i don't really know what's appropriate. i've only had one dom before, he was my fiance first, and i was way more into it than he (he would have never approached anywhere near my limits, so no safeword was necessary). online only, i always thought if anything was too much you could just shut the window or ignore it. . .

so, is a safeword useful with an online dom? any other tips for me while i get started? thank you.