Convenience - While this is only one of the positive points of online stock brokers, it's certainly one of the biggest. Having a stock broker who is only available during the day may be okay for some people, but most are working, dealing with family and handling other commitments during "normal" business hours. Finding time to make contact with stock brokers who have only daytime office hours can be a real hassle.
But online stock brokers are available 24-7, even when the stock market is closed. Even when they're not physically sitting at their desk (and many of them won't be except during regular hours), you can leave e-mail, place orders and make plans for trades. Perhaps you're a night owl and you do your best thinking, planning and analyzing in the wee hours of the morning.
With an online broker, you can do your stock trading when it's right for you. Instant information - Most online stock brokers have some serious data at your disposal. They're used to doing business by e-mail and are going to have lots of stock market data available at any given moment. It's in writing - If you've ever wondered what you might have told your broker in a moment of "enlightenment," online trading could be just what you need.
There's no need to fret over whether you told him to sell at $25 or to sell 25 of your stock - you can simply go back to your e-mail and see what you told him. Instant communication - With an online stock broker, there's no need to stop what you're doing and run down to his office to sign a form to authorize the trade. Typically, your e-mail is confirmation that you approve the transaction.