This section from @tagrtrades recent blog post caught my eye:

I’m slowly trying to move from a scalper to a bigger picture trader. The biggest catalyst to this change was letting the subscription to my intraday scanning service lapse and focus on my pre selected watch list. Sure I miss trades, but I know the trigger points I’m looking for and don’t find myself shooting from the hip nearly as much as I have in the past. I’m also trying to look at charts outside of just the 1-5min timeframe I’ve done for years. Pulling back and getting a clear hourly view has helped me look for areas where I can target for more than just a few cents and get more % out of each trade.

I've had a few thoughts about the pitfalls of using a real-time market scanner:

Information Overload

Even when you really fine-tune your scanner, it's still spitting out dozens of things to look at every day. There's just too much to look at. I have what I consider to be an incredibly rigorous set of criteria that has to be met to qualify as an "Unusual Suspect," and still I get at least a dozen candidates every day (today I got 18). If you're looking at everything, you're looking at nothing. The human brain can only focus on a few things.

Pavlovian Response

Every time the scanner dings, you get excited and think about making a trade. If you're looking at an intraday time frame like the three minute chart, you're going to start overtrading. You'll be generating a lot of commissions and very little profit, if any.

Liquidity Issues

I use the scanner to find "Unusual Suspects" in real time. They are generally low float, micro-cap junk stocks that are on a tear, (or they are bigger stocks that have been hit with news, good or bad (earnings, FDA decisions, etc.)).

The trouble with the low float, micro-cap junk is that after the initial burst of activity, volume dries up and there's no way to exit your position in a graceful way, even if you're on the right side of the market. You get stuck. And I mean stuck at a profit. It isn't as simple as crossing the spread and getting out. If you have 10,000 shares of a dollar stock, or more likely tens of thousands of shares, you just can't exit without tipping your hand, and they'll move the market away from you fast. It's frustrating.

Dependency Issues

It's possible that you may shape your whole trading strategy around the scanner and grow overly dependent on it. I like to think that everyone should strive to be able to trade profitably while still using an old 14" cracked laptop on a dial-up connection from the Australian Outback.

Unnecessary Expense

I've always thought that your broker should supply you with a first-rate market scanner, gratis. My broker, IB, does have a pretty good market scanner, but it's nothing like Trade-Ideas, not even in the same league. Schwab probably uses the old CyberTrader technology for their scanner, but I really don't know. Fido, Schwab, TD, IB, etc. should all license the Trade Ideas technology and offer it to their "pro" users for free.

I might think of some more things later and update the post, but that's it for now.