Habs get more cash to spend (overspend) on players they might want to attract (UFA or RFA offer sheet) but, more Cap space for teams to keep their own UFAs (reducing the UFA pool Mon would have been able to tap into) or match RFA offer sheets.
MON might be tempted to make a play overspending on one UFA to address the weakness on D but, that's a double edged sword, with so many players looking to renew their contracts in the short term (pending UFAs and RFAs).
If nothing else, Bergevin has been pretty good at managing the team's Cap structure.
That's why I believe his 'perhaps we'll trade a forward for some help on D' transparency might be directed at Max Domi, whose upcoming contract as an RFA risks setting the mark for future contract negotiations internally.
Avoiding an overpay there and letting some other team deal with that contract negotiation can limit the ask with other Hab players going forward.
Personally, I'd overpay Barrie for 7 years (ages 29-35), move Petry for futures and flip Domi (ideally Drouin) for Girard in Colorado.
Two PP quarterbacks, one from the right and one from the left (who can actually play together on the PP if you want because Barrie has a strong enough point shot to be a trigger on his off side) to go with Weber and Chiarot next year, then Weber and Romanov the following year once the Russian D has tuned into the NHL's game.
Revamping MON's D this way in one offseason could seriously jump-start this lineup offensively and defensively, IMO.
Unfortunately, TOR may now have found the money to re-sign Barrie. Maybe they had an insider tip into how much the Cap was rising and this influenced how they dealt with Barrie, ultimately, at the deadline this year?