What is unsettled profit?
Unsettled or speculation profits refers to the day-to-day profits/losses on your positions. It keeps fluctuating as per your trading position as per the prevailing market prices. 

Why will you not be able to use speculation profits on T+1 day?

When you sell/exit Intraday equity trades, the Exchange takes T+2 days to credit the profits to a broker and thereby to your account. Hence, any profits used by you on T+1 could  lead to a margin shortfall which is liable to penalties. To protect you from such penalties, we have decided to discontinue the use of such profits on T+1 day  in your best interest.