There is a difference between spending to the cap and bad cap management. Unused salary cap space doesn't carry over from year to year, not using it is just as bad as using it badly. The best teams will maximize every dollar of space available to them without having to give away good players to stay compliant. In Toronto's case, this season's opening roster is just $4 short of the $82.5M salary cap with defenceman Timothy Liljegren's $1.4M on LTIR. That's some impressive math by Dubas and his cap expert Brandon Pridham.
If you think $4 in cap space is tight, you won't believe the Vancouver Canucks. Between LTIR and active roster usage, their 22 man opening night roster will have $0 in cap space. Not over the cap, not under it, but right on the nose.
There are several other teams that are extremely tight to the cap. Vegas has $17, the Lightning $33, and rounding out the top 5, the Oilers are just $165 short of the cap. If you've been wondering why salary dumps have gotten so expensive for teams this season, that's why. The flat cap hasn't stopped player salaries from rising, meaning there is less total cap space available than ever.
The Leafs only real cap casualty going into the season is Nick Robertson. Despite an fantastic training camp, the Leafs winger had to be sent down because of his waiver exempt status. We could see Robertson back up with the big team quite soon however, if Tavares can't play on opening night, the Leafs will have to dress 19 skaters. After playing 1 game a man short, they can use an emergency recall to bring Robertson back up without his salary counting against the cap. Whether Tavares starts the season healthy or not, I would expect to see Robertson up with the big club at the first opportunity available.