Following excerpt from a text says Figure a and Figure b are equivalent:
But in practice when Figure b is used we are recommended to use a 10k or upto 100k resistor between the inverting terminal and the amplifier ground. Otherwise saturation is observed.
In practice Vin can be a battery or a transducer which is powered by a galvanically isolated power supply.
Regarding Figure b why does this issue happen in practice even though Vin is floating? Why such resistor necessary?