I'll bite.
Say it's a payment app.
They can track every transaction you make, report oddities to the IRS, flag you for an audit. They can drain your account. They can blackmail you when you buy flowers for your mistress.
Get it?
The fed already have agreements with financial institutions that enable them to receive real or near time reporting.
CALEA laws are obligatory and since the gubmint spent money on the systems these companies use, those institutions must make easy access to any information they target.
Thing is, the feds can’t create programs to address the myriad of OS’ and Dbase that exist, many of which are proprietary.
So, they ask financial institutions for similar “whole pipe” access and they just trawl everyone’s information and transactions.
This app will be one more marker in the investigative process.
I’ll think about it’s usefulness to .gov and do a write up.