As @(name removed by moderator) said, you need to be mindful of where the sacristy is relative to the main body of the church and how voices might carry. I’ve been in churches where the two are no where near each other so it’s no big deal; in some where it’s located right behind the sanctuary, and thus, could be a big issue; and in others where you would be surprised. Two parishes near me have sacristies in rooms adjacent to the sanctuary; in the one, you would think it was far enough away with limestone/sandstone walls that the sound wouldn’t carry, but when the door is open, the voices echo out into the whole church! At the other, where it’s a closer proximity, there seems to be an architectural barrier that blocks all kinds of sound from reaching the main church - and I still can’t believe it as I type, but it’s always the case; a party could be going on in the sacristy without disrupting prayer in the church.