Here's exactly why the Shea Weber deal is beneficial to the Montreal Canadiens

"To qualify for LTIR, a player must expect to miss at least 10 NHL games AND 24 days of the NHL season.

When a player is on the LTIR, a team can go over the salary cap. Despite the common misconception, LTIR does not remove a salary from a team's overall payroll, it simply allows the team to exceed the salary cap.

The amount a team can exceed the salary cap due to LTIR is commonly referred to as the "LTIR Pool."

If a team meets the cap on Opening Day without using LTIR, or uses LTIR at any time during the season, the LTIR Pool is the player's LTIR Cap Hit minus the team's cap space when the player moves to LTIR. For example, if a player with a Cap Hit of $4M moves to LTIR when the team has $100,000 in Cap space, the LTIR pool is $3.9M ($4M - $0.1M). For this reason, teams often make several moves to their roster just before a player moves to LTIR in order to be as close to the cap as possible to maximize the LTIR pool.

If a team cannot be cap compliant on opening day without using LTIR, the LTIR pool is the amount the team goes over the cap. For example, if a team is $3 million over the cap and places a player on LTIR with a $4 million cap for the opening day roster submission, the LTIR pool is the $3 million the team is over the cap.

During LTIR, salary space is no longer accrued, which means that any unused portion of the LTIR pool cannot be used later.

When a player exits LTIR, the team's annual cap hit for that day must be less than the cap"

We didn't want to take the risk that if we got bad news with Carey and he wasn't able to play, that we'd be left with almost $20 million on the LTIR. That would have limited our ability to spend to build the best possible team on the ice." - Kent Hughes