Still, I have a 50mbps fibre line and don't personally need faster. I already stream 3 android boxes and do some downloading with capacity to spare. As an example of usage, streaming dstv now @1080p only takes around 5-8 mbps, netflix at UHD takes around 20 - 25mbps at most.It's just about better speeds. Depending on the configuration that snapdragon 845 chipset can get speeds in the Gigabit range theoretically. In a real world scenarios we should get over 100mbps easily.
In general 4CA would give out double the speed of 2CA if the same kind of config is used.
These speeds are important to me as someone who uses my phone as a hotspot for my pc at times and I am not covered by fibre in my area so LTE is all I have. Hence I need utmost performance from my devices in terms of LTE speed.