Suppose a retail daytrader has a $50k margin account, and let's assume its value stays above that level for the whole day. He wants throughout the day ideally have simultanously 5 positions open, each initially worth about $10k. If a position needs to be closed he closes it and wants to open another one. Now the question: Is there a limit (per regulations etc.) on how many total round-trip trades he can make on the same day? Ie. what happens with his DTBP when he closes a position? Will it increase back to previous levels? Another related question: what is different if that trader were an institutional daytrader?
You can use up to your full buying power all day long in and out of positions. When a position is closed your buying power allocated to that position is restored. If you hold position(s) overnight it will tie up your bp for a day or two, as I recall.
Since 99% of day traders allegedly lose money, I assume what you meant to ask here was: "What is different if that trader were an institutionalized daytrader?"