A lot more than with SMS. You can send someone an SMS but they are not going to respond because either they cost money or they have some tiny allowance of them.
Also I have a dumbphone and I am the only person my friend send SMS too. That makes me quite a unique person !
SMS only works if you live in a region where unlimited SMS plans are standard AND you don't have any friends outside of that region OR WhatsApp doesn't have market share there. Basically only US.