Second half of last season was more, if one full back goes, the other stays back a bit, right? But it's different this season and very noticable.
The only time I don't think I saw it happen was vs Southampton in the first half (think I will re-watch that half later), and I thought we killed it, but Klopp didn't seem to like what he saw from a defensive standpoint, didn't he? Hence the change.
I think we have the quality to play like how we did vs Southampton first half on a regular basis and dominate, even vs strong teams I'd rather see us take more risks tbh.
I think this is indicative of an evolving system, and also of the opponent.
We have a basic pattern of positions and spaces we want to attack/defend, and everything else works within them.
If we want teams to attack a particular flank when we're defending for instance, we will use a pattern of positions and spaces to encourage them down that flank, often using a flat (not staggered) midfield 3 diagonally, to push them to that side.
It works well when we encourage teams to attack TAA's side.
Oppositions often see a young player as a weak link and target them, not noticing that's exactly what Klopp wants them to do, which is why we so often see Salah stay high on that side with 2 of the 3 midfielders sliding over to not only help TAA, but also to regain possession in an aggressive defensive press, so that we can release Salah.
When we attack, our basic pattern is as I've described previously, but
because we use positions and space rather than a rigid "traditional" formation, it gives us fluidity that is difficult to defend against if the opposition are trying to pick up players that are constantly changing/swapping round (this is another function of the midfield, and Firmino).
When the opposition deploys a strictly zonal system, it makes life more difficult, and what we rely on are opposition errors, and it only takes a small mistake of a player leaving his zone, or not being in sync with his teammates to let us in.
For as long as Klopp is here, we'll see different versions of the same basic systems; tweaks if you like, but important ones, depending on the opposition.