Raw files can include an embedded jpeg preview. The embedded jpeg will reflect your camera's internal "secret sauce" for making images look great. Lightroom uses these embedded previews to quickly render a thumbnail right after import and then keeps working in the background build a replacement preview of the raw file itself. The raw file awaits your touches in the develop module, which hopefully can make it look even better than the jpeg.
Raw files are significantly more flexible than jpegs, but require time and attention for editing. There's a time and place for each file format. Although raw is highly regarded, there are conditions - such as live sporting events - where some pros shoot in jpeg due to processing time constraints. You might likewise find that your ideal file type varies.
