It's been a while since I researched this (accounting is not my strongest suit), but it always seemed like depreciation schedules for server/datacenter equipment were always super aggressive compared to usable life. For an expanding company, I would assume that for a high growth company with a high datacenter cost structure, this would mean that until growth slows down, net profit will always be "pessimistic" compared to the more abstract "health" of the company.
The aggressive depreciation schedules might be due to the more compute-intensive use cases. Most servers are replaced due to new technology, mainly power consumption improvements. Maybe for low power scenarios the ROI bar for replacement is a lot higher, meaning low power servers get used longer than average. I would expect that Dropbox mostly uses these (I would assume they are more IO bound than compute bound).
When I was working as an accountant, computers were depreciated with a three year life. It's important to understand that an assets useful life often exceeds it's depreciation schedule. If an asset is sold after it's fully depreciated, it's just recorded as a gain.
That's true, but it's also really hard to do for a new company or new technologies. Dropbox started on AWS, so they don't have much experience running their own datacenters. They'll probably adjust their depreciation schedule in the future when they know better how long useful life really is.
The aggressive depreciation schedules might be due to the more compute-intensive use cases. Most servers are replaced due to new technology, mainly power consumption improvements. Maybe for low power scenarios the ROI bar for replacement is a lot higher, meaning low power servers get used longer than average. I would expect that Dropbox mostly uses these (I would assume they are more IO bound than compute bound).