I can see there's been a lot of demand for the "ignore files/folders with selective names" feature, but Dropbox is yet to consider an implementation.
Largely, what this does is (1) save on uploading unnecessary folders (such as node_modules) that take unnecessary space; and (2) save on downloading uncessary folders when adding a new device for syncing.
And by the way, Selective Sync doesn't solve this problem - as user responses have shown.
Now, there's the Smart Sync feature that solves problem #2 in some way. However, problem #1 is still there. Or does Smart Sync solve this too?