It's a simple matter of convenience. Taxes are paid out of your paychecks and into the government every year. I'm pretty sure if you were just asked to write a check instead of have it automatically done for you, you would often times fail to do it.
This system would allow for clans that want to impose a tax on their members to do so without their players having to do it manually. That would be the ease of the system. And when I mention they wouldn't notice it's because this gold they already know is going to be given partially to the clan bank and the rest is theirs to keep. I am absolutely sure that with a tax system, my members don't mind 2-4%, hell, even some all the way up to 10% being removed from their ticks, but they would appreciate the tax more if it was automatically done for them without them having to calculate the expense.
All in all, it's a suggestion. The animosity it is receiving is somewhat unwarranted and the assumptions made about it while they may be sound in other circumstances are largely un-called for especially when you are considering to peg me as someone that would abuse this system when I for one would largely support it not only for KUTT, but for a multitude of clans to make it easier to gather funds for the clan and the armoury.