It depends. Classes can greatly help the understanding of a map. It ia much easier to recognise and identify few classes than it is to interpret a vast continuous scale. But really, it totally depends on your data and intentions.
It is easy to arrive at wrong conclusions. But it is No.1 argument against discrete scales, not for it. It can happen by accident, but it is possible also to intentionally deceive - e.g. by setting such bins that Greece and Spain have the same color but Italy do not. Or that Spain and Italy have the same (but Greece different), etc.