I've heard that the mobilized people are used as a sort of early-warning meatshield for the more veteran forces by from an intercepted call by Ukrainian SIGINT (ofc veracity cannot be independently confirmed), which gels with Russian BTG tactics as known to US defence before the 2022 invasion[0].

[0] "Defeating the Russian Battalion Tactical Group" https://www.benning.army.mil/armor/earmor/content/issues/201... (warning PDF link)