Here are a few specific categories where custom flyers for business promoting are a smart choice:
These are just to name a few. As a business owner, you won't want to miss out on the opportunity to really get the word out about these types of announcements and promotions. Word of mouth is just as important as your advertising campaign and flyer printing is a great way to get people talking about your business.
The major reason that flyer advertising is still one of the most popular forms of marketing is due to it's cost effective nature. It's hard for businesses, small and large, to pass up on such an easy way to reach their target audiences (because they can choose where they place the flyers) at such a reasonable cost. Mobility is also an advantage. You can pass them out, leave them anywhere with a bulletin board, give them out with each sale you make, etc.
You can certainly think of your own reasons to put together custom flyers for your business. Consider who you would want to target and what you'd say to them if you had their attention for 10 seconds.