OK
In the 320, DES mode, on profile, AP/FD pitch will maintain the profile, like the G/S mode maintains the glideslope.
If everything is perfect during the idle segment, A/THR mode will be THR IDLE.
If the airplane tends to get high, speed will increase as a consequence of increasing pitch down to maintain the profile. After reaching the upper limit of the speed range, the airplane will get high unless you intervene.
If the airplane tends to get low, then speed will decrease, up to the lower limit of the speed range, point at which the A/THR will become SPEED.
So in the 340, DES mode, on profile, the AP/FD pitch will maintain target speed, instead of the profile. So what does THR DES do? Does it maintain the profile? If not... Who does?
99Jolegg is right. If in the 320 THR DES is not necessary, why is it necessary in the 340?