I think it really depends on what the medical costs are where you live (just like with human insurance). I personally don't have any insurance, my regular vet costs (vaccinations etc.) aren't expensive and I have started an emergency fond in case something happens (it's small now, but in a few years it should cover about anything). But if I lived in a country where medical costs are very expensive and/or had a pure breed pet that is more prone to some illnesses, I would definitively invest in some insurance. It seems to me that just one serious treatment would cover a lifetime of insurance payment in some places.