Porosity refers to the object’s ability to absorb water, which is done through capillary action. This is a serious concern when talking about pottery, as overtime it can weaken the body of the piece that is naturally made out of clay.
This should be taken into account when looking for the right piece of pottery, however the desired porosity of high-fired pieces should be around 1%-2%, making the issue less severe. This being said, in the case of low-fired pieces, the pottery should be coated with a non-crazed glaze. That is done to reduce the water absorption rate.
It must be said that those factors don’t mean that low-fired pottery is subpar, but it might not be ideal for certain uses.