Hello hurricane51,
Thank you for your questions.
Smart rendering means lossless cut and join, keeping the original video quality while the editing thanks to that the video is not re-encoded if you use trimming only.
So if you make only splitting, editing of your files by removing unwanted fragments, it works without re-encoding, so the output quality will be preserved.
If you use other features of the Video Editor along with editing (adding audio, pictures, text overlay), then there will be re-encoding only in those places in the file where these elements will be used.
If the edited files with different parameters, then the different ones will be re-encoded
Due to the fact that the file is not completely re-encoded during the editing, not only the original video quality is preserved, but Video Editor also allows you to quickly complete the editing and get the resulting file.