To answer both of your questions, the reason is really two-fold.
First, when scaling into a position that takes several days or sometimes weeks to set up, you do not have the luxury of just closing it out on a whim and then re-establishing. So what you do is while you are building up the position, you always have your "hedge cord" ready to be pulled if necessary.
If the cord is pulled, and the hedge is applied, you then have the benefit of changing your net direction from long to short as easily as it was to lay on the hedge. Usually, once a hedge is applied and you are mathematically neutral, you can begin unwinding one side of the trade, and then go net whichever direction you want. However, if the move that caused you to pull the cord ends up having been a false move, you can the resume your campaign of building your position. In fact, you can even keep the hedge and simply resume expanding the original position, so that if you have to hedge, you can just add. Of course this reduces your risk and hence your return, but it's a good way to approach a choppy market. Then when/if you're ready to totally directional without any hedge, you can do so.
But I hope you can see that there are so many dynamics involved in having to put on larger size, that you should be grateful you only have to worry about 25,000 shares at the absolute most at any time in a stock like CSCO.
This is really why I love trading currencies and in fact spend more time doing forex than I do equities. You want liquidity? There's real liquidity there. There's more liquidity in any given day in the majors than in ALL of the stock markets around the world combined.
Pejman Hamidi