I have lens corrections turned on as part of my default settings. That's what I have chosen to do because it works for me. I made that decision after examining some of my images. You will just have to decide what works best in your situation.
Lightroom sliders work just as well on JPEG images as they do on raw images. There's nothing that should be ignored just because you are working on a JPEG image. The only problem is that the JPEG is much less flexible. And while you can make adjustments on that JPEG image, they probably won't be as effective because the JPEG image is only 8 bits, all of the camera settings have been "baked in" to the file, making your adjustments less effective.If you understand the difference between working with a film negative or a slide then you might understand the difference between working with the raw file or a JPEG file. The JPEG is like working with a slide. What you see is what you get, and it's not really very easy to adjust it. The negative always gives you much more flexibility in processing. That is the benefit you gain when shooting raw.