It refers to a person who will go to great pains to save a few
Pennies here and there, but think nothing of spending a large sum
of money on something they do not need.
'Penny-wise and pound foolish' means to be careful with small
amounts of money, but careless when dealing with large ones.
For example, someone who is careful to save small amounts, but
spends it all on short term, wasteful things, could be described as
being penny-wise and pound foolish.
This means a person is careful or wise about little decisions
but may not be careful about bigger ones. Like someone who would
order a salad with low-calorie dressing, then follow it up with a
super-duper ice-cream-laden double chocolate cholesterol fest.