Like any files, Hero Lab portfolios can be saved and loaded directly to/from Realm Works. However, with this new integration, you'll be able to do something even cooler - integrate an encounter from Realm Works directly into Hero Lab.
Let's say your players run into some monsters, which are stored in a portfolio in Realm Works. You want to start a combat, so previously you'd need to get the portfolio out of Realm Works, find it on your computer, import the monsters from it, then import the player characters too, before you could get started. That's a lot of steps to go through.
With this new functionality, you simply press a button on the encounter in Realm Works, and Realm Works sends the file to Hero Lab behind the scenes. Hero Lab then immediately offers to import the monsters from the encounter, which you can confirm with a single click. That saves a bunch of time, which helps keep the pacing up, as well as removing a bunch of boring tasks that you'd have to do otherwise.

You can keep the player characters loaded in Hero Lab, and integrate each encounter as needed, then delete the slain monsters at the end and prepare to integrate the next encounter.
I'm not sure if this functionality is switched on in Realm Works yet, but once it is, you should see a new "Integrate" button beside each saved Hero Lab that lets you do this.
Hope this helps!