A tricky subject and I suppose it depends on how much you can afford to not make a claim, and how frequent treatment is required.
We have resisted making claims for George who is now in his eleventh year for any bills under £100 for the usual non specific stomach bug/ ear infection sort of problem, yet I would claim for one off type of problems such as a self limiting injury if the treatment cost went much above that.
We have always treated the insurance as the backstop for any serious and expensive treatments that may arise.
The situation arose in the last few months with bouts of acute pancreatitis and gall bladder issues, the cost of ongoing drugs is over £50 per month and treatment has cost over £1200 thus far.
This is the sort of thing we took the insurance out to cover.
Up until George was nine we used to shop around annually for pet insurance and usually made savings, but now of course with his age and current problem we are stuck with the current insurer.
At least the monthly premiums are less than the monthly cost of his treatment, and he is also covered for other complaints.