What I am going to describe is based on my personal experience and without IT knowledge. Call it perception if you like.
As I have experienced a number of times, my monthly quota of 4 GB for Rm68 can easily be used up within a day or two if I viewed some video clips even sparingly. Therefore, it is a luxury which I reserved for when someone who needs to use it.
Recently, when my daughter said she will be back for Christmas, but will be 'working from home', I topped up 1.25 GB for Rm20. I had already used up my quota and it was 5 days before end of the quota month. She used her notebook to access databases as well as to communicate with her colleagues in Bangkok via Skype. Just one day before 'end of the month', I received the usual notice about '80% quota used up...' followed soon after by '100%...' Fortunately, she could continue her work without complaining about slowdown as was expected when quota had been fully used up and speed was throttled.
This apparent 'no change in speed' soon after notice that 100% quota had been used up, made me wonder if YES's system had been unfair in notifying customers earlier in the hope that they will top up immediately. The fact that my daughter's work seemed uninterrupted despite notice of quota used up even made me wonder if she could have used the internet connection without me having to top up in the first place! Why do I have this impression? Simply because, for the current month, my quota was already used up within 2 days, yet based on throttled speed, I could access and use Maybank's online share trading system for almost 2 weeks already. YES, unlike Maxis, does not specify the speed under throttled mode. Maxis states 128 kbps (used to be 64 kbps). Instead, YES notifies 'fair usage policy is enforced'...'you can continue to enjoy unlimited data usage with reduced internet speed'.
This led me to another question unanswered: When additional quota had been purchased, any use of memory would seem to include the presumed let's say, 128 kbps which is supposed to be free under reduced internet speed. This would effectively speed up the usage of the additional quota. Again, this helps to fuel my perception of unfairness.
To illustrate, I use the analogy of a friend's complaint about massage charges. For eg. standard massage is Rm50 per hour. He was asked if he wishes to have an additional type which uses a spoonlike thing to scrape hard on his back. Not understanding Mandarin, he was presumed to have agreed. After the massage, he was charged Rm95! When questioned, he was told that the additional charge was for the special type. But by having the special, it would seem he had to forgo the time meant for the standard massage.