RAM, which is an acronym for Random Access Memory, is used to store parts of active applications so that they can quickly be accessed by the processor. It is considered volatile memory which means when the power goes off, nothing is saved in RAM. Consider it a place for very short term storage, which allows you to multi-task with your phone. Compare this with your device's native storage, which stores complete files and is much slower than RAM.
To prove that more than 4GB of RAM is unnecessary, Mr. Lao points to the Apple iPhone 7. The Huawei executive notes that the iPhone works as smoothly with 2GB of RAM (3GB on the Apple iPhone 7 Plus) as any Android handset sporting 4GB of the stuff, thanks to optimization with iOS. The executive says that piling on more than 4GB RAM on a smartphone does nothing more than needlessly jack up the price.
We should point out that this thought could change in the future. Back in 2014, Huawei's chief of consumer business, Richard Yu, said that 2K resolution screens were unnecessary. Yu said that people could not tell the difference between FHD (1080 x 1920) and QHD (1440 x 2560) on a smartphone. But that changed in April 2016 when Yu said that Huawei would start producing phones with 2K resolution. Sure, Yu said that it was necessary because of upcoming VR capabilities, but the point is that something did happen to make Yu change his mind.
Perhaps some feature that is unknown to us now will eventually require smartphones to carry 6GB or more of RAM in order to work right. The bottom line is that even if there doesn't seem to be a reason right now for a certain technology to become more powerful, you never know when that additional power will be needed.
source: LaoShi (via weibo) via AndroidAuthority