Odesa is the major Black Sea seaport for the Ukraine receiving over 40 million tons annually.
A sea blockade isn’t any guaranty that the coast and seaport is completely sealed off. All military and civilian imports will continue until that seaport.
It is taken and its facilities used to service Russian needs.
Further inroads into the Ukrainian interior can originate from the seaport of Odesa and only add to Zelensky’s problems.
If it is Putin’s intension to reconstruct the defunct Soviet Union by reacquiring the former states along the western borders of Russia, capturing Odessa affords not just an almost complete control of the Black Sea but a closer means of initiating an invasion of Moldova.
Currently there are 1200 Russian military personnel assigned to Transnistria as part of a join peace keeping force after the Transnistria War, 2 November 1990 – 21 July 1992, but also to protect a huge Russian arms supply depots in Transnistria.
The capture of Odessa then would be the debarkation point for Russian forces assigned to invade Moldova.