Initially I didn't like character replacing since I was just a child when it first happened and I disliked seeing one of my favorite characters leave and be replaced by an annoying newbie. Then it got worse when Dawn came.
However, now I'm okay with character replacing since I've become much older and become easily bored with watching the same people do the same thing over and over. I need new characters with different goals and personalities to add a scene of freshness to the show. Not to mention seeing a large variety of Pokémon on the main cast. So I truly am happy that characters do get replaced once their saga is over.