I've often wondered why everyone feels the need to purchase their own set of five Aravos for the Hoshana Rabba rite. Why can't one simply Qlap his neighbor's Aravos five times on the floor? An Esrog/Lulav set is somewhat different in that one gets much more use out of them during Hallel, Hoshanas etc.
According to Tanya Rabbasi [#86] "After Davening, each person carries home his Aravos and places them at the head of his bed to show his great love of the Mitzvah. This is the appropriate practice."
The Rama in Shulchan Aruch [664:9] writes: "The Qustom is to keep Aravos from HR until Erev Pesach and then use them for firewood for baking Matzos. Thus what was once used for a Mitzvah, will again be used for a Mitzvah."
HaGahos Maimoneous states that "the Rivak followed the Qustom of reusing the Aravos from SuQQos as Quills for writing a Sefer Torah, or as firewood for burning Qometz on Erev Pesach."
Finally, the Menoras HaMaor [3rd Candle 4:6:7] writes "The Aravos used on HR are a Segulah for protection during one's travels. Their effectiveness depends upon the righteousness of one's deeds and the purity of his intentions, He who trusts in Hashem will rest in his shade."
So my thoughts are that in order that one have Aravos to place at bedside, or use as firewood for baking Matzoh, or use a Quill to write a Sefer Torah, or use as firewood for burning Qometz or take on his travels, he should purchase his own set. Yet my thoughts wandered further that since most people don't follow any of these practices, one can simply gather the remains of another's Hoshanas for all these purposes. Of course, there is more sentimental value to use one's own object for these various Mitzvah's/Sequlos. And since the cost is relatively cheap, I suppose one should continue to purchase their own Quota of Aravos.