They're rarely even that much. To the extent that a lot of the time futures rarely even get cashed in or recognized as being part of a subsequent move.
There are a handful of instances where the futures do come around in some significant way (IIRC the deal that sent Theo Fleury from Calgary to Colorado included futures that ended up being the rights to recently drafted prospect Robyn Regher, where he was conveyed like a month after the actual original trade. If I'm not mistaken the theory was that Calgary basically got a list of prospects and was told "pick one, we'll give you some time to decide." and FCs was the way to engineer that grace period. I also believe there was some claim that Jeff Buekeboom being traded by Edmonton to the Rangers was the fulfillment of the future considerations in the Edm-NYR deal that sent Mark Messier to New York) but most of the time it's basically something of such little value that it can't be documented. Because if you were going to give them a 7th round pick or something like that you'd just do that.
I believe most recently the biggest use of futures was pre-expansion-draft trades where the future considerations dealt by Vegas/Seattle to other teams were "we promise to select/not select <insert player> in the expansion draft.
In terms of how futures mostly end up being a big fat pile of nothing of value for an NHL roster or prospect pool, most famously, the Jets 1.0 traded Kris Draper to the Red Wings for futures. Those futures quite literally ended up being $1. Other times it may be used as a stand-in for things that the teams are not legally allowed to trade each other, like there was a minor league trade where a team dealt a guy and got back appliances for their equipment room, or a WHL trade where a dude was traded for futures that ended up being a used team bus that the club receiving the player had and the trading team needed.
If the futures in this deal end up being anything of any real value I will be shocked.