The Leafs have briefly sent Stuart Percy down to the AHL a few times this season, before recalling him to the NHL shortly afterwards. It appears as though they've begun doing the same thing with Sam Carrick. This has led a number of fans to wonder what exactly the Leafs are doing. So what are they doing? They're trying to maximise the amount of space they have available under the salary cap. Let's take a look at exactly how that's happening.
How the Salary Cap Works
Each NHL team's spending against the salary cap is calculated on a daily basis. The NHL season is considered to have 186 days, so for each day that a player is on an NHL club's active roster, 1/186 of their cap hit counts towards the team's allowable spending for that season.
According to Capgeek, Stuart Percy's cap hit for this season is $863,333. That means that for every day he's on the Leafs' active roster, the Leafs lose $4,641.58 against their maximum spending on player salaries for the season. The converse is also true: for each day he's not on the active roster (ie. in the AHL), the Leafs gain $4,641.58 that becomes available to spend later in the season.
Over time, this money can add up. If Percy were to be off the roster for 40 days this season, that would free up 185,663 additional dollars to spend elsewhere (such as on trade deadline acquisitions). That might not sound like a lot, but for a team like the Leafs that operates near the maximum allowable spending, that money could prove to be very helpful. And now that the team is doing the same thing with Sam Carrick ($3396.06 per day), the savings compound.
[NOTE: The preceding section initially had math based on a 185 day season. James Mirtle of the Globe and Mail informed me that this year the season length is 186 days. The math has been updated to reflect this error.]
So Why Carry More Than The Minimum Allowable Roster For Some Games?
When the Leafs are playing home games, there's probably not a very good reason to. The Marlies play just down the road, and if a call-up is needed, they can arrive almost immediately. But when hockey teams go on road trips, it can be difficult to get players from the farm team to an NHL arena in time for a game, especially if there's an injury in practice on the day of a game. So most teams prefer to have at least one spare forward and one spare defenceman on the roster for road games so that there's always a player available to step in if an injury occurs outside of a game.
This advantage is available to the Leafs primarily because their farm team and their NHL club play in the same city. Many NHL teams can't do what the Leafs are doing to maximise cap space.
The Leafs May Not Be Able To Do This All Season
Some NHL players can be assigned directly from the NHL to the AHL. But many others, either because of their age or the number of NHL games they've played, have to be placed on waivers before they can be sent to the AHL, which gives other teams the ability to take them for free. Most of the Leafs roster would have to go on waivers to be sent to the AHL, and the Leafs obviously don't want to lose most of the players they have under contract.
At the moment, the Leafs have three players on the roster who can be freely sent to the AHL without worrying about waivers: Sam Carrick, Morgan Rielly, and Stuart Percy. The Leafs are unlikely to send Rielly to the AHL, however, likely figuring that as one of the team's rising stars, it's better to keep him happy by paying his full NHL salary rather than saving some money against the salary cap.
If all the forwards on the roster are healthy, including David Booth and Joffrey Lupul, the Leafs would not have any forwards who can be sent to the AHL without passing through waivers, so they would lose some ability to maximise cap space through call-ups and demotions. But Stuart Percy will remain waiver-free all season, so the Leafs are likely to continue passing him back-and-forth between the AHL and NHL for as long as they believe he should be the team's 7th defender.