They don't lose value every day they gain value as they become more scare. Lower supply = increased price per unit assuming constant demand.
What XRP is is explained here: https://ripple.com/knowledge_center/math-based-currency-2/
The use case for XRP is explained here: https://ripple.com/xrp-portal/
Briefly, there are 2 main purposes of XRP:
1. It serves a bridge currency. It is a foreign exchange asset that is aiming to be liquid with any currency. If you're trying to convert one currency into another you will sometimes have to go through multiple intermediate currencies and every exchange exacts a fee. XRP theoretically shortens the exchange path for most currency pairs. Also, there is no counterparty risk so no risk of someone defaulting. You own your XRP as much as you own the $100 bill in your wallet. In contrast, the money in your bank account is actually an IOU. The banks is saying that it owes you money but could always default on it's obligation.
2. Distributed ledger systems have transaction limits. Last I saw Ripple's was ~1000/second. If it's free to transfer XRP you could imagine a malicious spamming attack to slow or prevent efficiency of the system by setting up bots to transfer XRP back and forth at a high rate. To prevent this, Ripple has implemented a fee system whereby every transaction costs some amount of XRP. The XRP is permanently destroyed. As such, XRP holders are likely to only submit legitimate transactions to the network which promotes and efficient system.
My personal opinion is that Ripple currently has shown the most real world adoption by banks. Banks are currently using the Ripple network to transfer fiat currency. Ripple has the most robust compliance controls in place which matters if you want real businesses to use your network. XRP is currently relatively cheap but the price is expected to go up once they finally shut down Ripple Trade and more banks come online in the second quarter of this year. At that time they will announce an incentive structure for Market Makers to provide fiat liquidity to the Ripple network...
The amount of currency, cryptocoin, digital asset, or token that any company creates is a bit arbitrary. Depends on the use case but if you're an early speculator you care more about the % increase in value then in the absolute value of the token.