What does the mobile phone traffic security package service mean?

According to the principle of normal deduction, after the resources contained in the traffic package are used up, it will be charged at X yuan /MB, which is much more expensive than using the package. Taking Guangxi Mobile as an example, the 300-meter traffic package in 20 yuan is launched, and the charge is 0.29 yuan /m after 300 meters are used up. If 100M is used continuously, it will reach the extra charge in 29 yuan. If Anxin package service is launched, when the excess charge reaches 10 yuan, the charge will be suspended until the excess flow reaches 100m. For example, the original excess charge1kloc-0/m will be 29.29 yuan, but with Anxin package, the charge will only be 10.29.