The Falcons are sitting on plenty of cap space, and some of that will go toward their incoming rookie class. Just not a ton of it.
Over The Cap has an excellent article breaking down rookie salary pools and how the actual cap hits are often misunderstood, and it's worth reading. The upshot is that NFL teams really don't have to dedicate all that much in the way of salary toward their rookies, and that means the Falcons have more cap space at their disposal than we've assumed up to this point.
The Falcons, then, are looking at a rookie pool of $6,267,517, with an effective cap cost of $2.77 million. That's not a ton of money, and it means the Falcons can and should utilize the rest of their cap space smartly to set themselves up for success in 2015 and beyond.
If the Falcons tell you they're hoarding cap space for rookies, in other words, don't believe them. It's much more likely that money will go toward a Julio Jones extension, a couple more free agents and perhaps will be kept to roll over in 2016, a year when the Falcons will now be down a fifth round pick. The ability to roll a heavy cap charge for Julio into this year
How do you expect the team to use the rest of its cap space?