My position on this one has changed over time (fortunately slowly enough that it hasn't confused my poor dogs too much).
I used to add "Stay" as a double command after every position change, so it would be "Sit-Stay" or "Down-Stay" or whatever. I didn't have a particular reason for doing it this way, it was just a habit I developed.
In some competition venues, you get dinged for that because it's considered a double command, so I stopped doing it that way and cleaned up my cues to a single command. Now the "Stay" is implied, so I usually just give the position cue (sometimes I have to add a "Stay" for clarity depending on the exercise, as it's not 100% faded yet and can be helpful depending on the total context of what we're working on).
I still teach and use "Stay" separately to mean "freeze right now in whatever position you're in, and don't move" because I find that helpful for getting the Stand out of Motion (it can be tricky to differentiate from a default Sit otherwise) and also when the dogs happen to be in an arrangement and position that I want to photograph while out hiking. I haven't yet gotten to the point where they will freeze perfectly -- they tend to settle into the nearest taught position equivalent -- but it's a goal that I work toward sporadically. We may or may not ever get there, I dunno.
ARCHMX TDCH Pongu the Insane, CD-C, RE, RL1X6, RL2X5, RL3X2 (GSD mix, b. Apr 2010)
Crookytail the Tigerwuff, RL1, ITD (Akita mix, b. Jan 2011)