Despite being able to experience Witcher 3 on its own merits, playing The Witcher 1 and 2 can definitely enhance your overall understanding and appreciation of the world and its lore. You'll get to witness character origins, develop deeper connections with certain individuals, and have a richer context for some of the events taking place in Witcher 3.
Ultimately, it's up to you to decide whether to play The Witcher 1 and 2 before diving into Witcher 3. If you want the complete narrative experience, including the full backstory and character development, playing the previous games can be rewarding. However, if you simply want to jump into an epic adventure without prior knowledge, The Witcher 3 stands strong on its own as a fantastic RPG, regardless of whether you've played the earlier titles in the series.