After editing a full video, have you ever found when saving it youv'e wasted
like 20 mbs, does anyone here have ideas or ways to compress the file before saving ?

What do you mean wasted 20mb while saving it?

You mean exporting the movie or just saving the project?

when saving and exporting

Well for exporting, only way to get a smaller video file is by making the resolution smaller or setting the quality lower.

But for saving I'm not too sure about.