Suppose you own the following shares of some particular company like, say, Microsoft, using two brokerage accounts: 50 shares @ $20.69, account #1 50 shares @ $19.37, account #1 50 shares @ $18.12, account #2 50 shares @ $17.76, account #2 Suppose further that you can live with holding on to all of them, but you'd rather just keep 100 of them and sell off the rest IF you can do so without losing money... if only because that money can then be used to buy more, cheaper shares in Microsoft if the price keeps falling. Now... let's suppose it's tomorrow afternoon. The market is rallying HARD for no sane reason, and by some direct miracle of God, Microsoft is trading for $19.51/share... but it's obvious that it's not going to last, and the price is going to crash any second. If I want to sell 100 shares, would I be better off selling my 100 cheapest shares at a profit, or selling my 100 most expensive shares at a small loss?
All things being equal, you always sell the losing shares to avoid paying taxes. All things being equal, realized gains and unrealized losses is just plain stupid.
It makes no difference. There is an important difference between tick backed and cash backed trades, however. If you are up on a trade but haven't taken profits, you are ticked backed. If you feel that your ticked backed trade will lose ticks / go against you, you should sell. Then if your right you can buy back shares at a lower price, and be cash backed from the profits you took. (this really applies more to futures than stocks, though)