Whilst an unfinished door may sound like one that is a missing a pane of glass or two and has a bunch of pencil lines left on it that you need to cut around yourself, it is obviously not quite as unfinished as all that.
There are positives and negatives to buying doors that have not yet been painted, stained or varnished, and the one you choose will often usually depend on how much work you want to do yourself. With internal doors you can actually leave them unfinished should you have found the perfect door for you that fits in perfectly with your decor. However, that does leave them more prone to wear and damage, as well as at the mercy of temperature and atmospheric changes.
External doors on the other hand should always be finished, either at the place of purchase or by yourself as they will be at the mercy of the elements day in and day out.
So, when looking at internal or external doors is it better to buy them finished or finish them yourself? Well, the bonus of unfinished doors is that you may well get a much better range of options, meaning that if you find the perfect design you can paint it or stain it the exact colour to fit in with exactly what you want. However, this does mean that you will have to spend the time painting and/or staining the door yourself.
So ultimately whether you want external or internal doors, the choice of unfinished or pre-finished will usually come down to just how much flexibility you need and just how much work you want to put in yourself. On the other hand you also have the option of finding an unfinished door, and asking the company to paint and varnish it in the exact way that you desire.