increaseAllowance adds to an existing spending permission rather than replacing it, which makes a large grant less obvious.
increaseAllowance exists to fix a real problem with approve: changing an allowance from one non-zero value to another can be front-run. Adding to it instead avoids that.
The consequence is that the number in the payload is not the resulting permission. It is the amount being added to whatever is already there, so a small-looking value can still leave a large total, and a large value achieves the same thing as an unlimited approval without ever showing the familiar all-Fs number.
Treat it exactly as you would an approval: check who the spender is, and check the size of what you are granting.
Check a transaction of your ownPaste anything. It is decoded in your browser.