What makes Bitcoin worth it for my savings? That it increases in value.

Will it increase in value if there is no demand for it? No.

What gives it demans? Utility.

I don't mind buying my groceries using LettuceCoin but what if it takes me 3 days to convert bitcoin to LettuceCoin? Do you think I will keep very much in Bitcoin or do you think it would have lost its utility for me?