Most banquet tables are 29''-30'' high, which is standard dining height. These tables are great for just about anything - eating, displays, raffles, banquet service, head tables, you name it.
At the same time, the only bar-height tables you probably already own are cocktail tables, which are most commonly found in 24'', 30'' or 36'' round styles. Great for a couple of drinks and an elbow here and there, but not ideal for a lot of your utilitarian tasks.
Bar height banquet tables are super useful for a variety of tasks. Think about the last time you had to plate 300 chicken dinners. Not having to hunch over to wipe down the rim of each plate is really nice, and your back will thank you.
Not only that but think about charity events with a large amount of silent auction items on display. Wouldn't it be nice to put the delicate items up behind the first row, for a multi-tiered effect?
Or even for something as simple as a trade show. If you have a lot of giveaways and don't want kids running off with all your logo pens, a bar-height table will really come in handy.