So just to prove above lets do few calcuations with HRC:
Here would be basic nash ranges: http://hands.holdemresources.net/?id=1wldx2f2y6c3u
BU shove 19.6%, 55+ A2s+ A7o+ A5o K9s+ KJo+ Q9s+ JTs, BB call 10.6%, 55+ A9s+ A9o+ and SB shove 28.1%, 44+ A2s+ A3o+ K9s+ KTo+ Q9s+ QTo+ J8s+ JTo T8s+ 98s, BB call 13.1%, 44+ A7s+ A8o+ KJs+.
If we use FGS1 (one hands into future) expection would be that both BU and SB will shove tighter even though BB will also call tighter: http://hands.holdemresources.net/?id=1oqk5nzdil1eg
BU shove 19.0%, 66+ A2s+ A7o+ A5o K9s+ KJo+ QTs+ JTs T9s, BB call 9.7%, 55+ A9s+ ATo+ and SB shove 25.0%, 55+ A2s+ A5o+ K9s+ KTo+ Q9s+ QTo+ J9s+ JTo T9s, BB call 11.5%, 55+ A8s+ A9o+ KJs+.
Now if we lock calling ranges from BB into nash ones so we would assume BB is not adjusting to villains tightening little of their ranges: http://hands.holdemresources.net/?id=ykl3hm7mnj2t
Now BU will shove 12.2%, 66+ A5s+ A9o+ KTs+ and SB shove 13.0%, 55+ A7s+ A5s A8o+ KJs+.
So basically because of next hand likely allin from CO shove ranges dropped considerably for mid stacks. BU from 19.6%, 55+ A2s+ A7o+ A5o K9s+ KJo+ Q9s+ JTs into 12.2%, 66+ A5s+ A9o+ KTs+ and SB from 25.0%, 55+ A2s+ A5o+ K9s+ KTo+ Q9s+ QTo+ J9s+ JTo T9s into 13.0%, 55+ A7s+ A5s A8o+ KJs+. I would say those are huge differences.
Another common situation where FGS will differ is when coming blinds will hurt your stack considerably. E.g. lets say you are UTG with 5bb. Dropping from 5bb to 3.5bb after blinds will drop your fold equity lot so shoving bit wider from UTG to try and keep your stack alive make sense. Even though in vacuum certain hand would be somewhat -EV to shove. Also in above calculations CO shoving range does widen from 17% into 27%

