I quilt on a long arm machine so the quilting is fairly close. I may be sorry one day, but I just butt my batting together and quilt it....no extra stitches or tape. As for whether I would use it under white fabric...I'd test first. It will depend on how see through your white fabric in your quilt is. I don't buy the almost see through whites. I don't like my seams showing through the fabric. And, yes, I don't have hardly any white in my stash. Almost all of it is too thin for my taste.
I do use a white batting for light projects. Beige batting for medium colors or something with a lot of beige background fabrics, and black batting for those intense fabric combinations. Beige will make white look dingy and I don't like that at all.