Are you playing 21? The offensive linemen have a resistance bar which goes up every time a DL attempts a move. So, on first down you come out in a regular 4-3. The RE (Let's say Jerry Hughes) goes outside on a spin for example. On 2nd down, you come out again in a 4-3, the LT now has a point of resistance outside against
Hughes specifically. Now it's 3rd down and you come out in Nickel with Hughes at RLE. Now he is on the opposite side, lining up against the RT and the RT does not have resistance points against him, making Hughes' move more likely to succeed.
If you keep Hughes in the same spot all game, the offensive lineman will eventually develop a ton of resistance and start to shut him down. The resistance system encourages you to sub guys in and move them around.
I can't really speak to franchise, I am an online guy exclusively, but maybe I can explain this a different way.
Let's say that on First down, you come out in a 3-4 Solid with no coaches adjustments against regular I-Form Close.
Imagine we're looking from the usual camera view behind the offense, your guys will line up like so
#2CB - #1FS - #1SS - #1CB
#1ROLB - #2MLB - #1MLB - #1LOLB
#1RE - #1DT -#1LE
Ok, now imagine it's 3rd down and you want to come out in 3-3-5, now it looks like this:
#2CB - #1SLCB -#1FS - #1SS - #1CB
#3SUBLB - #1SUBLB -#2SUBLB
#1RRE - #1RDT -#1RLE
So you can see how the back four of the secondary are still drawing off the original depth charts but the front seven are now pulling from the specialist depth charts.
Two important notes: 1)
specialist depth charts have priority. So if I put in Micah Hyde (my #1 FS) in as a Slot Corner, he'll play Slot Corner whenever its on the field and my #2 FS will come off the bench to play FS. The lineman specialist packages AFAIK have priority over the SUBLB, same deal.
2) Specialist depth charts are
activated by the formation you pick, not game situation. So if you come out in a 4-3 on 3rd and 20 for whatever reason, it's going to roll out your normal lineup even if that's your run-stopping group.