It totally depends on the music you’re copying, there can’t be a general answer to theese questions.
Flows allow you to have flow headings, tacets (exclude some instruments from one flow), independent Notation Options, independent tokens in the templates… You can use flows typically for different movements in a piece, or for different pieces in an album, or for exercises books…
If the music never stops, if you don’t need the above mentioned features, then probably there is no reason to divide the piece into different flows.
But if the music is in significant sections, one can have them play straight through without a break by eliminating the delay between flows in Playback Options. The only catch is notes tied over from one flow to the next; that would require special handling.