See attachment here on bulk deals of 13.09.19 it shows same company buy & sell shares of Dewan housing , I don’t get it , what it means?
They Provide Liquidity.
Bulk deal is a trade, where total quantity bought or sold is more than 0.5% of the number of equity shares of a listed company. Bulk deal can be transacted by the normal in trading window provided by brokers throughout the trading hours in a day and brokers have to immediately notify the Exchange. Bulk deals are market driven and take place throughout the trading day.
In this case, it’s just a case of scalping or day trading, just like we do except that it’s done on a larger scale. 
But if u calculate stt & other charges for that trade it wud never be profitable than whats meaning of this