Performance on old, slow desktops of installed apps versus on a USB drive

I am wondering (when using an older, slower computer) if it would be better to use the default, installed media viewer, or the portable VLC that I have on my USB drive--not in terms of graphic performance and the quality of the display, but in terms of slowing down the old computer itself.

When I am working on an older, slower computer, I am a bit conscious about not slowing down the computer to the point of it freezing up or something like that.

(1) Is there a general consensus about showing an MP4 from my USB drive, with the portable VLC or say, Windows Media Player that is installed on an older desktop? Or is it a matter of, if the computer would freeze with one program, it would freeze with the other?

(2) Would copying the files to be displayed, onto the desktop computer itself change anything? If I copy pictures or videos onto the desktop computer and then show them, would that make it less likely to freeze up the desktop computer?