It's definitely one of my favorite shows of all time and it's a good time for a rewatch.
Reading the wiki, you can see how it had the GOAT filming style. Most scenes were filmed in one take. Instead of having the actors stand still, they were allowed to move and have the cameras follow them. Plus, if an actor had input on how a line should be delivered, he/she could change it up.
One of the main producers of the show even said that FNL was what he imagined filmmaking to be before he got into the film industry.
Here's an excerpt from the wiki
Though scripted like any hour-long television drama, the show's producers decided at the outset to allow the cast leeway in what they said and did on the show, including the delivery of their lines and the
blocking of each scene. If the actors felt that something was untrue to their character or a mode of delivery didn't work, they were free to change it provided they still hit the vital plot points.
[14]
The freedom given to the cast was complemented by the fact that the show was filmed without rehearsal and without extensive blocking. Camera operators were trained to follow the actors, rather than having the actors stand in one place with cameras fixed around them. This allowed the actors to not only feel free to make changes but to feel safe in making those changes, because the infrastructure would work around them. Executive producer Jeffrey Reiner described this method as "no rehearsal, no blocking, just three cameras and we shoot."
[15]