What do you intend to buy if you sell? If you want to buy back in lower on the same stock, then you may end up increasing your position once you take into account brokerage. Often, many people end up employing a dual strategy where they have a core LT holding in a stock but will also buy trading parcels to try and take advantage of price fluctuations to bring their overall average cost down. Depends on how good a trader you are though and how closely you can watch the market. For some examples of this at work look at the 5 grander thread where as an example @minoil and @TheArchitect are nimble with their entries and exits and have built up quite the nice kitty starting with $5k.
