The one disadvantage to buying your coffee already ground can sometimes be that the coffee you get isn't always completely fresh. Once you grind a coffee bean it will immediately start to lose freshness and may - in a bit of time - simply not taste as good as it did when you first bought it.
So, if you buy bags of ready ground coffee in a shop you may find that they don't taste as fine after a couple of months as they did when you first purchased them.
A common solution to this is simply to buy your coffee from a store that will grind beans for you on the spot and then bag it up. Brands such as Starbucks and other barista outlets, for example, will be more than happy to do this service for you so you can enjoy all the advantages of using ready ground coffee with none of the shelf life disadvantages.
Another thing to remember is that ground coffee doesn't just come in a single version. You can often specify the kind of grind that you want for your beans. The kind of grind you get will usually be tailored to suit the way you make your coffee (i.e. - the way your brew your coffee or the type of machine you use) - basically you can look at anything from a fine to coarse grind.
There probably isn't a quicker or more convenient way to make a freshly brewed cup of coffee than with ready ground coffee. Remember - if you shop around a little - you can find all kinds of unusual and exotic blends to try.
Also see espresso machines for more details.