Personally I dislike it very much. It take feel of achievement. Why even bother with gaining experience if it makes enemies stronger?
It depends. When done correctly it can be fun, if all creatures/enemies are always scaled to your level, no. Dragon monsters for example should always pose a challenge or some kind of monsters that are you mirror images/copies, that type of thing. Maybe it’s your rival or someone that has far more experience then you do, why wouldn’t their level also grow?