It’s quite unlikely, but I can indeed imagine a situation where you’d want to buy a naval base in a landlocked area.
Let’s say it’s Russia’s turn, and there are some valuable British units in Kazakhstan (say, planes), Novosibirsk is empty, and the Japanese hold Timguska where they have a strong force of tanks and mechs that could destroy the British by blitzing through Novosibirsk. And the situation on the board is such that Russia doesn’t have any units available that it could send there to block Japan.
Russia can then save the British units by building an air base in Novosibirsk, but that would imply giving that base to Japan for free. So the better choice for Russia if the rules would have allowed it, would have been to build a naval base there, which contrary to the air base, can never be used against the Allies after Japan takes it.