I don't know the details of Pakistani law, but it seems like it could be a clever judicial technique for fighting corruption or tax evasion in cases where it cannot be directly proven. If you spend more money than you lawfully earn, then presumably the rest have to come from illegal activities (assuming no fortune)?
For example, we had a governor that had as wages about 10000 usd month... yet was spending millions.
Not even the craziest bank would fund that, so it must have been corruption. (It was, he received if I remember correctly about 100 million usd in bribes)
In India, you can. Having assets dispropotionate to known sources of income creates a presumption of corruption, plus one can also be charged for tax evasion.
You can be charged for living beyond your means?