We've officially moved past the point where Doom 3 is a glorified doorstop on Switch to where all that fluff is optional.
Not content with leaving retro releases well enough alone, Bethesda dumped a ton of new school functionality into their old school Doom releases, leading to a bevy of memes regarding a Bethesda.net account requirement. Now, it's an option that will get you free stuff.
Doom 3 specifically just got a "minor patch" (1.03) that is live now on all platforms. If you decide to sign in to your Slayer's Club account you can net the "Red Doom Marine Skin," as well as a Doom 3 nameplate for Doom Eternal when it hits in 2020. Harmless cross-promotion ahoy! You know someone in marketing is really proud that they thought of this.
Doom 3 1.03 [Gearnuke]