Why do teams do this?
Although the NHL has mandated a minimum of six exhibition games per team prior to the start of each regular season, that doesn't mean all players that make the Opening Night roster have to play in all six.
The team will have over 40 players at this year's training camp, but of course, only 18 skaters and two goalies can play per game. Simple math means that if you were to divide the playing time equally, most players would only play in three out of the team's six games.
Over the past few seasons, we've seen that the Canes take this route, which also allows them to prioritize keeping players healthy over forcing them to play six games in 11 days, before embarking on an 82-game journey over the coming seven months. Additionally, it allows players competing for spots within the lineup to adequately showcase what they've got.
NHL rules do state that teams must dress a minimum of eight "veterans" for each preseason game, but the league's definition of a "veteran" is loose this time of year. Any skater who played in 30 or more NHL games in the previous year qualifies, as does any goaltender who dressed for 50 or more or played in 30 or more games.
On top of those players, a first-round draft pick from the most recent NHL Draft qualifies as a "vet" for the purposes of preseason roster building, as does any player with 100 or more career games. These standards include playoff games.
So, to answer the above question, playing two games on the same day is essentially no different than playing games on back-to-back days. Players wouldn't play on consecutive days in the preseason, so having two different rosters go at it on the same day tackles two birds with one stone, or in this case, one plane, and in turn buys an extra practice/off day.
