TL;DRAn unlimited allowance lets the spender move every unit of that token you hold, today and in the future. It saves you a transaction on every trade. Keep it for apps you trust and use often; for anything else, an exact amount or a revoke is the calmer choice.
Where the huge number comes from
Allowances are stored as a 256-bit number. Wallets and apps that want an open-ended approval simply write the largest value that fits. Nullo shows any amount at or above half of that range as Unlimited, because no real balance comes anywhere near it.
Permit2 works the same way with a 160-bit number, and adds an expiry date. An expired Permit2 allowance is shown as closed even if the amount is still large.
The trade-off
With an exact allowance you approve again before every trade, which costs gas and an extra click. With an unlimited one you approve once. The price of that convenience is that a single problem in the spender would reach your whole balance of that token, including tokens you receive later.
There is no universal right answer. A router you use every day is a different case from a contract you approved once during a mint months ago.
A simple routine
Scan your address now and then. Sort the unlimited rows by how recently they changed. Keep the ones you clearly recognise, look at the hints and labels for the rest, and add the ones you do not need to the revoke queue. Each revoke is a separate transaction, so you stay in control of every step.
Try it on your own address
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