The Galaxy J7 Max features fast lenses for both the front and the rear cameras. The front comes with a F1.9 aperture lens and the rear camera with a F1.7 aperture lens. These are very bright lenses, resulting in better low-light photography capabilities. It's great to see that phone manufacturers pushing the cameras capabilities forward. Nowadays, phone manufacturers know that the front cameras is not less important than the rear camera, for some people even more than the main camera. Even saying "main" camera is misleading, because for many people the front cameras is their main camera, not the rear one.
Now, Samsung understand this and it wanted to make sure that you can enjoy high-quality photos using either. The Samsung Galaxy J7 Max therefore comes with a 13MP resolution camera for both the rear and front. This is a very high-resolution cameras that ensured that you get very detailed photos. Samsung went even further, and made sure that both cameras can capture high-quality photos also in low-light as well. Nobody wants to be limited by just being able to shoot in daylight. People want to get photos that looks good at night as well.
The utilization of a F1.7 and F1.9 lenses ensured that you get much better results this time around. Samsung also added both a rear and front LED flash to improve the image quality when shooting in restricting lighting conditions. The aperture of the lens is a very important factor that has a direct implications on the low-light capabilities of the camera. It's not the only thing obviously, but a slow lens just restricts the amount of light, resulting in a poor image quality when shooting in less-ideal lighting conditions, like at night or in an indoor place with very little light source.
In many other phones you've probably notices that you either get a good rear camera or front camera, but bot both. Sometimes phone manufacturers prefer investing more in the rear camera because they want it perform better. The reason that you can't have two superb cameras is obviously the price. Even with the Samsung Galaxy J7 Max I'm sure that Samsung cut some corners to allow these two fast aperture to exist in this phone. Maybe the camera image sensors are less expensive or maybe it cut out some other phone features that are not related to the camera. The thing is that you can't expect to have it all in a Rs. 17,900 (~276USD) mobile phone.
That being said, I have no doubt that these camera will perform admirably well, but I would have wished the Galaxy J7 Max came with lower resolution sensors, rather than a 13MP ones. A 13MP sensor also means that the pixels on the sensor are very small, which will definitely have a negative impact on the low-light performance. As I told you, it's not just about the lenses.
Another advantage that you get with faster lenses is a more prominent shallow depth-of-field (DOF) Bokeh effect. It's usually more prominent when shooting close-up shots. So it's good to have a faster lens for the front camera, because it helps blur distracting background elements out of focus better than a slower lens. All in all, I am happy with the lens choice in this phone.