I have to say that I didn't expect any of the next upcoming nova phones to have a 20-megapixel front camera. We usually see this high resolution for the rear camera, and even there it's mainly Sony sensors and you can find it on Sony Xperia smartphones. The previous nova Plus that was released on October 2016 came with a 8MP f/2.0 snapper, much lower resolution than the new nova 2 Plus offers.
That means that you get selfie images with maximum resolution of 5120 x 3840. I think that Huawei just put a great deal of attention for making this phone appeal to selfie lovers. You can see that the camera also include Beauty 4.0 mode, Portrait mode, gesture shutter, all are meant to help you get that perfect selfie shot and make you look at your best.
by the way, this is not the first phone who "dared" to go with such a high resolution, the Vivo V5 and V5 Plus also sports a 20MP front camera. I say "dared" because having such a high resolution can impact image quality. This is why you see many phone manufacturers who prefer going with a lower resolution sensor with larger pixels so you can get good image quality when shooting in low-light as well, not just in daylight. Of course that yet to be seen.
One of the disadvantage of this camera is that it has fixed focus, not autofocus. This means that it should capture your face sharp when you hold the phone in an arm-length position, but from my experience with fixed-focus phone cameras, it can sometime produce blurry results if you hold it to closer or further from the focus distance that the camera can produce a sharp image.
The Huawei nova 2 Plus front camera features an f/2.0 aperture lens which should help in promoting better low-light selfies, but keep in mind that it doesn't have a front LED flash, only LCD flash. I don't know which sensor the nova 2 Plus uses for the front-facing camera.
Of course having a 20-megapixel front camera has its own advantages. You can take very detailed photos of yourself or a group photos and even make large prints due to its very high resolution image. You have more room for editing the photo in photo-editing software as well. Having said that, most people just enjoy sharing their selfies on Instagram, Facebook, Twitter and other social networks. So 20MP is just an overkill for that. I think that Huawei just did it because a higher megapixel resolution is still seen by many as an index of measuring the camera's quality, but of course this is far from being accurate and there are many other features that need to take into account.
So no doubt that this high 20-megapixel resolution will make the nova 2 Plus stand apart from the rest, and a higher resolution does mean that you get a more detailed image when shooting in ideal lighting conditions. So in that regard, the nova 2 Plus have an advantage over its competitors. I really want to see how this translates to low-light performance, but this is for another entry which will be either slot into the advantage or disadvantage section, we just need to wait and see.