Tl;dr on this article is that a private valuation is more than a number. The whole picture must be considered. A high valuation with onerous terms might be "lower" than a lower valuation with reasonable or especially favorable terms.
One thing I don't get is: isn't a lower valuation on good terms better for founders? Why are founders playing the unicorn game at all?
Then there's the potential that the founder has taken money off the table (giving up on-paper money for cash), so even if the deal isn't quite as nice as it could be, they still own a significant portion of a "successful" company.
Also, the higher the top-line valuation, the more free marketing you get (the headlines read the same, just with a bigger number in it). This can translate into an easier time of hiring, and the ability to hand out smaller and smaller slices of equity for that top talent (employees generally will never see the term sheets to understand that even their 0.01% of the company is likely to be worth very little).
Obviously some founders will optimize for the former (lower valuation for better terms); others will be more interested in ratcheting up that top-line number to attract future investors, high-value employees, book deals, press, etc. That's ultimately the founder's prerogative.