Although they should not be relied on entirely to keep you up-to-date, alerts serve as useful reminders, and save you having to continually repeat the same search. For a busy scientist they are an absolute necessity. They are usually easy to set up, and can be sent to you in a variety of ways. You often need to amend your search terms after the first few results are delivered, in order to control what you are being fed.
A bonus in getting alerts, if you get them from different databases, is that you can find out which database best fits your subject or search terms, or sends alerts to you earliest.
You can get alerts sent to you for a variety of types of new development, for example:
You can get alerts sent to you from: