JMich: The same that any digital signature has. To ensure that the file is the one it should be.
Hm, maybe we should ask GOG to stop signing the installers. It is a check that the installer hasn't been tampered with, which means they don't trust us not to tamper with them.
As for wine and mods, not sure how well wine plays with denuvo (would depend on what kind of checks denuvo does, and whether wine plays nice with said tests), while mods would depend on mod implementation. A mod that can be added as a stand alone file (see Shadowrun Returns UGC or The Sims extra content for examples) wouldn't care about denuvo, while mods that required you to change the game's files would. So I do see denuvo as a means to create games with better mod support instead of worse.
But I may be an optimist in that regard.
you don't understand what is denuvo. It's not what you think.
denuvo is not a simple signature, uses an encryption system, is a signature control, continuous monitoring and forced.
one thing is to check the integrity of the installer, another thing is to check, every time, if the software is still intact.
if they had used such a system in the past, it would have been very difficult to adapt some games to modern systems (It is something that should not be underestimated).
Furthermore, there is no way of knowing if they entered a control software (or something similar) maintaining denuvo.
I do not underestimate, and I do not trust, the creators of securom.
Denuvo, does not allow you to know what's really inside the executable (.exe for windows).