Let me tell you in two ways.
If you just use the upcoming Path of Exile 3.19 expansion as a daily after-get off work pastime, then I don't think you need to prepare POE Currency in advance.
But if you're an avid fan of Path of Exile, then it's worth buying a lot of POE Currency for the 3.19 expansion.
At the moment we only know that Grinding Gear Games may release the 3.19 expansion on August 12th. The current Sentinel League may end on August 9th. And we have to learn as much as possible about the new challenge leagues and find good sellers who can provide us cheap & safe Path of Exile 3.19 expansion currencies between August 9th and August 12th .
As a veteran player who has played Path of Exile for six or seven years, whenever a new league is released, I am well prepared. And my best helper is POECurrency.com. Every time I am happy to Buy Exalted Orbs on this site such as Exalted Orb/Chaos Orb/Orb of Fusing etc.
Fast delivery, great service, fair price! If you want to Buy POE Currency in advance, check this website now!
But if you have your own ideas, you can do it too! I hope my answer can help you.