According to Reuters, the Kremlin needs 'elections' to demonstrate support for the war from the Russian people. The expected victory of the 'United Russia' party could serve as a convenient argument for the authorities to show the election results as evidence of public backing for the continuation of military actions.
Experts note that the Kremlin may use these elections to justify new decisions, including potential mobilization. Preparations for mobilization in Russia are already underway, despite public statements denying the necessity of such measures.
Additionally, for Putin, this presents an opportunity to showcase a picture of 'normal life' to Russians: elections are taking place, customary political rituals are being followed, which implies that nothing extraordinary is happening. The government may also use the voting as an argument in its confrontation with Ukraine, claiming that elections are happening in Russia while they are absent in Ukraine due to martial law.
After the election results are announced, Reuters suggests that Russian authorities may move towards harsher repressive measures, as the need to maintain pre-election optimism will have passed.