I don't completely agree with that. Depending on what type of business you're making, the best way to get work done is to go to conventions, because that's the only time you can easily meet with a bunch of people that are related to your industry and make new partnerships, check out new hardware/software solutions to save time or money, possibly hunt for some new talent to join the company, discuss business propositions, etc, can all be possible in much shorter period of time than doing the same outside the convention.
Even just having the opportunity to meet someone face to face that you've been doing business with for the past several months can be useful.
That being said, you don't need to go to a lot of them. Attend only one or two of the most productive ones per year (most productive ones are not always the largest), and you should get a lot done without spending too much time at them.
Also don't go if you're strapped for cash, as they're often expensive (depending on the industry). They're not absolutely necessary, and they can be a waste of time if you don't utilize them properly. But they can be helpful tools.