biennially

In terms of wildlife, there is no downside: the chestnut produces a larger mast than oak/hickory, and it produces every year instead of biennially. Its nut is starchy rather than oily.

The pertinent sentence from the methods section of this study is "Questionnaires have been completed biennially to update information on potential risk factors and occurrence of new diseases." Poor data in leads to poor data out.

I assume vision plans, which often include large purchase credits for eyeglasses at least biennially, are also tax deductible benefits. The result is often relatively price-insensitive consumers who "have" to spend $200+ on glasses lest they not be taking full advantage of their benefit.

They responded: "Unfortunately, at this time if you have any Linodes that you pay for annually or biennially, enrolling in the metered billing beta will remove your discount, and the process of changing over cannot be reversed."