I bought the Gear S2 Classic when I still had my Note 5, right before the Note 7 released. Used it with both of them, and then again with the N5. Altho by then I was sick of re-setting it up (and would also lose some data each time), I had intended to use it with my N8.
However, right around that time I noticed an indentation on my wrist, exact where the heart rate sensor is (green laser). You can have the HR monitor record your pulse every hour or every 10 mins. I have some cardiac issues so I had it set to take my pulse every 10 mins, round the clock (except for a daily 20 min shower). I want to say I used it for about 6 months before noticing the indent.
Thought at first it was just from pressure, but it's now been around 8 months since I've last worn it, and it's still there. There's a fitbit topic about it (would be the same cause), but I've never found anything on the Samsung watches.
https://community.fitbit.com/t5/Charge-HR/Indentation-on-Wrist/td-p/928148
Someone in that topic likened it to laser lipo, lol. Funny, but it maybe actually true.
I FLOVE that watch and am seriously pissed that I can't use it.