Cell Upgrade (Sid Meier's Civilization: Beyond Earth)

The following question has come up (which has been tormenting me since the 3rd part, which I decided to ask just now) - If I tell a worker to automatically improve the cells, he improves them at his own discretion. The question itself is - On what basis does he decide what improvement is necessary or unnecessary? For example: I have half of the territory under my control built up with "Earth Landscape" which requires 6 units of energy SIX ALL!!! I already have a small cash flow, but here it is ... Some more cells with resources are not improved by workers at all! Well, all sorts of things.
PS I know that many people will say manually improve it, they say it's more interesting, but firstly it's long and tedious, and secondly, AI still knows better than me what improvements are needed.