I don't consider the positioning of the trim reset helpful, beyond recentering your stick's center when using a non-FF stick when it gets all out of whack.
There is one instance that it works wonderfully. If you have two engines out and need to autorotate, if you don't want to go through a conventional autorotational descent, I found out that the Ka-50 in BS2 will act as a "parachute". If you allow the Ka-50 to enter a vertical or near-vertical autorotation, and then max out the collective and reset the trim, the aircraft will somehow maintain stability and a controlled vertical auto-descent and land soft enough for you to survive. It will collapse the landing gear, but will nonetheless be survivable.
I tried this multiple times. Each time the rotors slowed down to dangerous levels until enough downward velocity built up, the rotors will cone to an extreme, and the aircraft will kind of sway back and forth like a leaf sometimes. If you don't have the gear down, or can't lower it, don't try this cuz you'll just explode on impact. I would also recommend jettisoning your wing stores to make yourself lighter.
This whole procedure goes against all my real-world experience in helos, but I've never flown or had any knowledge about coaxials besides what's in the DCS BS manual. Whether the real-life Ka-50 can do this, no telling.