Sometimes you need one page as a picture: to put in a slide, to paste into a chat, or to show someone quickly.
A page exported as a JPG is a picture. The text cannot be selected, searched or read by software, and it is no longer acceptable anywhere a document is required. For pasting into a chat or a slide that is fine, and for submitting to an office it is not.
Resolution decides whether it is usable. An image exported for the screen will look soft if someone prints it or zooms in, so export larger than you think you need when the page has small print on it.
If you are showing only part of the page, export it and then crop. That produces a tighter image and avoids making the reader hunt for the relevant paragraph.
Export the pages and keep the one you want. Splitting first also works if the document is very long.
No. An exported page is an image, so the text becomes part of the picture.
No.