just had new cambelt and tensioner fitted, oh and new oilfilter( had not been changed for ages) can someone please explain why?

1. The exhaust has gone from unbelievably loud to sweet but still throaty,
before it was too loud, used to deafen me.

2. The car idles better

3. the car does not get as hot

4. the oil pressure is higher

5. the car pulls better, accelerates better.

I am at a complete loss, it is like a new car...WHY??