It used to be that only brokers with access to a stock ticker could get anything close to real-time quotes. This lasted through the 1950s and 1960s, when dinosaurs still walked the earth and most individual investors had to buy a copy of the Wall Street Journal to do all their stock watching.
When computers began to get connected to what would become the World Wide Web, there was a ready-made population of highly-motivated investors who were eager to follow the gyrations of their stocks. When markets get active, either frisky (to the upside) or cranky (to the downside), I suspect that all financial sites probably register a big increase in visits from nervous investors whose moods change as their holdings soar or dive.
Stock watching probably doesn't do any harm, but it does reveal something about you as an investor. Some people enjoy it, in the same way that some people follow America's Cup yacht racers or Tour de France bicyclists on a real-time tracker. But for lots of people, the intraday ups and downs of their stocks are an emotional roller coaster that can cause real distress.
I think that the emotional toll taken by intraday price fluctuations is one reason some people choose to become buy-and-hold investors. If you tell yourself that your investment horizon is five years, you can insulate yourself from the bruising that markets can give.
As a growth stock investor, my investment horizon is considerably shorter. The portfolio I manage (for Cabot Emerging Markets Investor) can turn over as much as 300% a year, so I need to take daily moves very seriously. And if you have a portfolio with lots of jumpy, speculative stocks, you may need to keep tabs on intra-day movements. But in general, there are only a couple of situations in which it makes sense for you to be following the stocks in your portfolio in real time.
The first is when your stock's company is reporting earnings. Reactions to earnings disappointments are so severe these days that a delay of an hour or so can make a significant difference in whether your investment finishes in the black or in the red. It's often prudent, especially in stocks in which you have very little profit cushion, to put a stop on the stock a few points lower than its pre-announcement level. Look for a price that's below the stock's normal daily fluctuations and place the stop a point or two lower. This will sometimes whipsaw you out of some stocks that react badly and then recover quickly, but more importantly, it will get you out of some stocks that collapse and never recover.
The second spot that's appropriate for intra-day stock watching is when you're trying to buy into a stock. If you have access to real-time prices, buying a stock at the bottom of its normal trading range can be the difference between a quick gain and an initial loss, and if you can catch one on a significant pullback, it can be quite profitable.
You might also want to use your stock watching behavior as a kind of psychological test to decide whether you're cut out for the life of an aggressive growth investor. If you find that a drop of a few percentage points in the price of your stock is genuinely distressing for you, then you might think about moving toward value investing or a more buy-and-hold growth style.
I know people who weigh themselves every morning and then feel either good or bad about themselves all day based on the result. And I'm sure that stock watching can have the same effect on some people. So ask yourself how hovering around your stocks is working for you and adjust your behavior accordingly.