while i do not disagree with trees being in all the time (this does not hurt the shoes), but my opinion is this: you dont have to put trees in shoes you have just purchased, are new never worn. if you are going to store these shoes, you dont have to have trees in them. as trees are meant to protect the drying and retracting phase of the shoes after they have been worn for a period during a day.
also, the crucial time to have trees in them would be right after shoes being worn (unless they are drenched in rain or other liquid) and up to 24 to 48 hours thereafter. after that, leaving the trees out will not hurt the shoes at all i believe.
cedar trees are meant to maintain the proper shape firmly while the worn and stretched shoes retract, but must retract properly. also the trees will wick some moisture out, but the main release of moisture is through natural evaporation. but another main thing the trees do is to provide a self cleaning effect, while the shoes dry the trees prevent the accumulation of bacteria and mold inside the shoes (this was the main destruction of my shoes in past years before i went to trees).
sort of like a swimming pool towel: after swimming and usage of towel , you do want to hang the towel flat and to dry fully before you roll it back up for storage (if you intend to use it again regularly). putting a wet towel rolled up in storage will make the towel hard and crackly, give opportunity for mold to grow on the towel, and thus destroy the towel.
let me add that a fair substitute for trees if you do not have some is rolled up tissue paper or newspaper. this can help absorb moisture better than cedar trees if your shoes are drenched. but remember to pull out the newspaper and throw them out as leaving them in there after the shoes are dried will make the newspaper exposed to mold, moisture to wick back out into your insole, and insects like silverfish and roaches. roaches like stacks of old newspaper.