What version of Premiere Elements and on what computer operating system is it running? It will not influence my answer but will give me information in case I need to get into version specifics to detail my answer further.
Timeline rendering is a preview matter. It does not fix anything, but it is your window of opportunity to catch of problem sooner than latter. If the Timeline rendering indicator displays orange (11 or higher) for the line above the Timeline content, that is the project telling you that you are not getting the best possible preview of the playback of that content in the Edit area monitor. And, every time you edit a file, you have altered the file from the time before. So, if you want to see the best possible for what you now have, you Timeline render. This is particularly helpful when you are dealing with titles, effects, transitions, and non native formats. You cannot turn off the Timeline render indicator system, at least none that I have ever found nor seen reported. You can do selective Timeline rendering by having the gray tabs of the Work Area Bar span only the Timeline segment that you want Timeline rendered.
Consequently, you either ignore the Timeline render indicator system, move on in the project, and take your chances in the outcome or you Timeline render to get your best possible preview if the Timeline render indicator is suggesting that you do so.
I am not approving or disapproving of this project feature, just commenting on the what is.
This is not Adobe. Rather user to user. If you want to have your voice heard at Adobe, you might consider filing an Adobe Feature Request Bug Report Form.
Add On...it is also possible to do Timeline rendering in a project, save close the project, and reopen it to find your previously "green" lined content now "orange", indicating unrendered. Yet the preview files generated originally by Timeline rendering are still existing in their hard drive save location. That is another story for other time.