Qualcomm Quickcharge doesn't turn off the charging completely, but instead it provides smaller current when the device is finishing charging. The problem with turning off the current completely is that LiPo batteries often report a little big higher charge level, so while it reports 100%, it could be anywhere between 90% and 100% in reality. The only way to calibrate the battery so that it shows the correct level is to FULLY charge it, despite it showing higher level. So if that charger stops providing current after getting a 100% report from the battery, this will result in a tiny bit shorter battery life with every charge. You won't notice it at first, but it will become VERY noticeable after a year or so also, the process becomes irreversible at some point, because a battery starts losing its true capacity if you don't fully charge it once in a while. It also loses capacity if you charge it too long, so reducing the current when it's finishing charging is a smart solution, because it makes this decay much slower.
A good example of overcharging is my tablet: I used to leave it charging every night, and sometimes throughout the day, too. After 3 years of usage, the battery lost 40% of its capacity. My mom's laptop is in a similar situation, because she basically keeps it plugged in 24/7, pretty much since she bought it right now the battery life is ridiculous. Something like 20 minutes, if I recall correctly.