Yes, there are scenarios where it is win-win.
These are niche corner cases, at best. They certainly don't explain the widespread fascination with day trading on cex.io.
1. A buyer wants to invest in coins but has a hard time going through the hoops at Coinbase and other purchasing outlets. Many have had buy orders automatically blocked by Coinbase's automatic algorithm, or may not want to wait 4 days for bank account transfer, or may not want to pay high fees for instant credit card transfer, or may not want to go through the verification process that takes 1-2 days (depending on how long it takes your credit card online to show you pending charges). Mining contracts are a different vehicle of translating fiat to coins, though sometimes at a premium.
(A) It's not like mining is going to give you a faster turnaround than coinbase, unless you invest HUGE amounts of BTC into GHs
(B) I was not under the impression that cex.io took fiat payment for GHs. Is that not the case? If they don't take fiat, then your scenario is pretty much moot, as you need BTC (or some other coin) in order to buy GHs in order to... mine BTC. And you certainly won't get back as much BTC as you put into it via mining rewards alone.
2. Seller wants cash delivered by different means that BTC withdrawal. Or seller wants to be paid NOW up front for time-value-of-mining. I had to pay for service on my car so I could drive to work. I had maxed out credit cards but was able to quickly sell 30 days of mining for an agreed upon price. Like a futures market, buyer takes on some risk based on difficulty and BTC value calculation (assume operational risks don't exist to simplify the analysis); and seller accepts guaranteed money NOW.
(A) I think most sellers only take BTC (as per my point B above)
(B) Seller getting money immediately is definitely a motivation, but probably only if they've already run the numbers and discovered their hardware won't ROI. If the seller is in a cash crunch, sure. There's some advantage there. If the seller can wait it out, they'll be ahead in the long run just by mining with it.
3. Buyer has coins with a pool or exchange and needs to increase the balance in order to reach the minimum for cash out. This is usually not a large sum of money but is a common scenario.
Given that cex.io until recently could only mine on ghash.io (and I'm not even entirely sure they've even allowed that change yet) then your point is largely moot. Even if someone had a small balance
at ghash.io, this still does not account for even a fraction of the cex.io traffic.
4. For large corporate players that buy ASIC gear and rent it out, assuming they have hardware on hand and aren't playing the pre-order scam game, they not only get money up front that they can then re-purpose it. This was the reason why progressive shares worked before ASIC wait times put all of them out-of-business, or forced the into high risk buy-pre-order-and-pray strategies.
Frankly, I'm not sure I even understand what you're getting at. Could be I've had too much wine, or it could be that it doesn't make any sense.
I will leave out the fraud and tax evasion reasons but you do see buyers with these motivations paying "over market value" for mining contracts.
Oddly, that might be the most compelling reason to use cex.io that I can think of.
