The choice is up to you whether you should go for an espresso machine with a grinder or not. If you already own a coffee grinder, then you don't need an espresso machine with its inbuilt grinder.  Again if you prefer to use ground coffee, then an inbuilt grinder will be useless for you. But if you like to grind your coffee before you consume it (and this is the best practice for better-tasting coffee), then you should choose a machine with a grinder.