This opportunity was absolute necessary as since 1 January you need to authorize the card transactions with 3DSecure, some sort of SCA (Strong Customer Authentication). So practically AutoTopUps like the ones from Revolut are somewhat "illegal":
https://www.reddit.com/r/Revolut/comments/kvn31m/auto_topup_is_no_longer_working_since_3d_secure/
So how this functionality it is helping you? Simple, you can define the fallback cards that can be used instead the ones that have no money in it because you didn't autotopup on time. More details here (experience is a must);
https://www.curve.com/features/anti-embarrassment-mode/
https://www.facebook.com/curvebg/videos/856447988499980/
https://support.imaginecurve.com/hc/en-gb/articles/360016571938-How-do-I-set-my-backup-cards-up-