No matter how experienced....
Scott crossfield once punched an aircraft through the back of a hangar because although he had read the aircraft's manual, he hadn't been checked out by a pilot who was experienced in the aircraft. If it can happen to him it can happen to you.
The attitude "I'm good enough and experienced enough that I can fly anything" is arrogant and is likely to get one killed. I think it's important to get training on any new type because humans aren't omnipitent, and even small things can cause accidents.
That being said, I do think it can be taken to extreme. At one flying club in the london area the policy is that if you haven't flown one of the club's aircraft of a specific type in the last 60 days (45 days for pilots below 150 hours) then you have to have a checkride in it. It doesn't matter if you've been flying another club's PA-28 50 hours in the last month, you still have to get a checkride. Now that's extreme!