I remember when my friend bought a brandnew Yamaha TD-whatever, and he went on a ride with me and my girl. My girlfriend was riding a little thumper back then that leaked oil pretty bad. About a litre every thousand kilometers
When we stopped for a cup of coffee somewhere he noticed half of her leg, and most of the engine was covered in oil. He didn't want to drive any further with us because he thought it was the most dangerous thing he'd ever seen. After we explained him that she'd been driving it like that for a whole season, he reluctantly drove on with us.
It's basicallly a continuous oilchange when you think about it, so it must be good for the engine