I'm not going to bother quoting all the replies in this thread, I'll simply lay out what my thoughts are and if people want to read it then so be it.
Alright, so one of the first things I read was more about WHY is scav mode useful? WHY is it in the game? For a couple reasons, and possibly more we don't know about since the information hasn't been disclosed in full. One of the main points being they're part of the lore.
Why would I want to play as a Scav? Because it gives me an alternative to playing my PMC with no real "Loss" felt when I die, a lot of people here are complaining that Scav mode will be abused because there's no real Risk in it, and yet others complain(Not in this thread, I know that) that earning gear is too difficult and they have a hard time keeping gear, well then this is an option for the latter, not so much the former...
UNLESS, you have other reasons to play it?
Insurance System - Devs have talked about it a bit but not really divulged too much information. Back when Insurance system was first discussed, the devs noticed an issue, people could commit in-game insurance Fraud. Insure a weapon, take it in, drop it to a friend then die. Now, your friend has the weapon and you claim your insurance. Devs then suggested they might look into having it so that if you insure a weapon and it's not Looted then you'd get it back. Maybe they will add a way for Scavs to have the option to 'return' a gun to a PMC that they've found for a reward through the Traders. 'What reward would be better than a weapon?' you might ask, well, that we don't know for certain because we're still in Alpha, and lots of details have yet to be fully revealed.
I for one want to be able to change up the game play when I play as a scav, I will play out scenarios where I will befriend PMC's and help them make their escape for a possible reward from one of them (Or just making out alive with any loot I've gained while helping them) Or maybe I'll pretend to help some PMC's, in the mean time setting up an ambush point with other Scavs, trying to lure them into the trap we've set.
As stated by a couple other members and I will repeat again, we will have a TOTAL OF 3 PMC'S1, not just one like we have now... And if people in this thread are still surprised by that information then I'd have to take a stab and say you haven't done your research on a product you've invested in (Although, I will admit and agree that information is VERY scattered in these forums, I've been here awhile and keep ontop of all dev replies)
A second reason for having Player Scavs is so that the Scavs are always a possible threat, once you know all the PMC's are dead in raid you can pretty much do as you wish, especially if you have fort armor with a helm. Scav players will keep pressure on PMC's remaining in the area. 1 @Natalino, could you confirm this information for those still skeptical? Or correct me if I'm incorrect and it's now a Single PMC. I couldn't find a source for it being mentioned, remember it might have been part of the Tarkov Weekly interviews.
Side Note; if a PMC is Injured (i.e broken leg, bleeding) or has died there will be a timer associated with how long it will take to "Heal" that information has not been disclosed. (Can you confirm this as well?)