I think Dax means the new larger maps have this spawn system where neither team really has a predetermined fixed side. I think he also means it works well on the new maps moreso than the earlier Reach large maps. Its not really a new system by any means though
Spire for instance you might start on one side as a team but as you die and it gets crazier your teams may have switched sides (especially if their entire team streamrolls yours and takes over your general vicinity to many enemy players equals your spawn spot being booted out across the other way) hence you will spawn on the completely opposite side.
The bigger Spire spawn system is in contrast to say Valhalla in H3 you always spawn on your side (even if you're being spawn trapped and spawn on the middle rock 'escape' spawns that would still technically be your half if you cut the map down the middle)*
*Unless host switches.
All this is in contrast to Narrows that was side only spawning but after a patch changed to a more flexible side switching system (that is straight garbage in a 4v4-5v5 map thats all about map control)
Default Foundry is also another map that works on a more large map based system as you can spawn on either left or right side (not the side you originally spawned on) if the other team was holding down the back (rockets area) Because the map is so small the spawns were generally completely hated on by lots of people. Onslaught did a great job of fixing the spawns to side only but the small arena size and clear lines of sight led to a lot of spawn killing and people thinking the system was 'messed' when really it was one of the more perfect examples of a spawn system in H3.
The top of the cake for shitty spawns is Standoff. Videos of warthogs getting killionaires beautifully showed this off, yet Bungie NEVER fixed this travesty. Hell it wasn't even that bad of a map and I generally don't like large BTB maps. The rocks set up some great BR battles and yes Standoffs
If only they had a playlist manager who would have not only been focused on playlists and weightings but actual gameplay. (He made some spawn fix attempts but weakly and slowly - Examples: Blackout and The Pit)