Your question has nothing to do with LW beta so please don't post questions there unless you are using the beta & have a comment about it's operation. I moved your thread.

Be aware that everytime you preview a file, it leave a copy of the file called PREVIEW - (filename).(vid extension) in your incomplete folder. So after downlding the file, arrange the incomplete folder by name or date & delete the preview files.
Personally I just drag & drop the video from the incomplete folder onto one of my video players/double-click it. I use VLC for most previewing since it handles incomplete files very well.

Once a file is 100% downlded, LW moves the file from the incomplete folder to the downld folder or "Shared" depending on what you named your downld folder.

Preview files will be the same size as the file was at that moment of downlding & will remain in the incomplete folder.
eg: If you previewed a video that has a total size of 700 MB but it was only 10% downlded, then the preview file size will be 70 MB.

__________________
Imagination is more important than knowledge. -- Albert Einstein
Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
640 K [of computer memory] ought be enough for anybody. -- Bill Gates (1981)
The secret to creativity is knowing how to hide your sources. -- Albert Einstein
When facts don't fit the theory, change the facts. -- Albert Einstein
Religion keeps the poor from murdering the rich. -- Napoleon Bonaparte
The important thing is not to stop questioning. -- Albert Einstein
I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones. -- Albert Einstein
"A composer is a guy who goes around forcing his will on unsuspecting air molecules, often with the assistance of unsuspecting musicians." -- Frank Zappa
"Tobacco is my favorite vegetable." / "May your sh*t come to life and kiss you on the face." / "Scientology, how about that? You hold on to the tin cans and then this guy asks you a bunch of questions, and if you pay enough money you get to join the master race. How's that for a religion?" / "Communism doesn't work because people like to own stuff." / "There are three things that smell of fish. One of them is fish. The other two are growing on you!" / "Jazz is not dead, it just smells funny." / "The creation and destruction of harmonic and 'statistical' tensions is essential to the maintenance of compositional drama. Any composition (or improvisation) which remains consonant and 'regular' throughout is, for me, equivalent to watching a movie with only 'good guys' in it, or eating cottage cheese." / "Remember there's a big difference between kneeling down and bending over." / "The most important thing to do in your life, is to not interfere with somebody else's life." / "Rock journalism is people who can't write, interviewing people who can't talk, in order to provide articles for people who can't read." -- Frank Zappa
"The music business is a cruel and shallow trench, a long plastic hallway where thieves and pimps run free and good men die like dogs. There's also a negative side." - Hunter S. Thompson
The shy can light the dull dark room with life when their eyes mirror their inner sunrise - LOTR