For the first few years of my time playing EVE I refused to buy insurance. I felt like it was betting that I would die and lose my ship. My PVP philosophy at the time was that I should avoid dying at all costs and try to have a very high kill to death ratio.
That logic made sense then and still sounds like a reasonable plan now, right?
Actually no, it's probably the worst way to PVP in EVE because you end up spending all of your time looking for the perfect fight and not actually fighting.
Instead turn that on it's head and bet that you WILL die and lose every single PVP ship you have. If you don't you aren't taking enough risks.
PVP is about both winning and losing, the only people I've known to have very high kill to death ratios were people would wait days between fights because they were to scared to take any risks.
Great PVPers take risks... The best take calculated risks.
So if you are PVPing, you should be dying and if you are going to lose your ship, you should insure it. Pretty simple when you frame the argument like that.
But that's only PVP ships. Mining, Missioning, Hauling, and other ships don't usually benefit from being insured because they don't get killed as often.
Finally, be sure you insure T2 ships also. It used to be a waste of money, but the rates have changed and now it is worth insuring a T2 ship if you plan on using it in PVP.