Until 2018, when the value-added tax was introduced to Dubai, there were no taxes.Chiociolla/ShutterstockThe biggest money managers on Wall Street are shedding billions in stocks for this one tax strategy.Tax-loss harvesting allows investors to offset capital gains taxes by selling securities at a loss.Here's what you need to know about using a tax-loss harvesting strategy.It's officially stock-selling season, according to Bank of America.Institutional investors usually increase their selling activity towards the end of the year, and this year was no exception.