Recently, I have stronger impression of that dance should be easy and smooth. The foot work , the body rotation and the technique developed serve this purpose. Spotdance is a dance that 2 bodies dance as one unit. We design moving forward , backward, sideward, turning to enable the dance attractive . When we move laterally ( outside partner and maintain connection as well.) CBM ( turn standing side body toward free leg ) and CBMP ( footwork , one track or more than one track ( freet foot cross the standing foot a little bit) needed or occurred inevitably to serve the purpose mentioned.
Feather step on 4, shoulder leading is maintaing, so just put the free foot cross it without body turn, CBMP.
Here, it is established after 2 and 3 step. We have enough space to simply put the foot in progress ( feather step ).
More compact body connection may need stronger CBM and has a consequence of CBMP in side moving. such as 5 steps in tango. Correct me , if I was wrong. Thanks.

I think you mean step 3 of the feather - this is the step that achieves CBMP for otuside partner by keeping the same side in advance that was leading in step 2.

Step 4 usually features CBM to initiate a following reverse figure of some variety. While reverse CBM is felt more in the hips than shoulders (at least compared to natural CBM), it will still have the effect of changing which side of the body is leading.

CBMP means to step the foot across the body. In Tango the man has a strong left side lead so he does not have to turn his body to dance cbmp with his right foot. In the feather step in the foxtrot we use cbm(swing) to turn our body(side) so that we can step outside our partner from knee to toe only,while keeping our hips in line with our partner.

Actually tango is danced with a RIGHT side lead - you move towards your right side, it gets there first, so it is leading (check the figure descriptions). However, the normal leftward stretch must be maintained, and the two concepts are often confused.

See also the three step in foxtrot.

Sorry I should have said right side left leg,we curve to the left. I remember practicing the walks around a chair. The good old days.

CBMP is simply the abbreviation of'Count Body Movemnet Position'
It implies your current walking (both forward or backward) maintain a postion whereby the right hand swings forward while walking forward with your left foot and keeping your upper body slightlt swinging towards towards the left (or the left hand swings forward while walking forward with your right foot and keeping your upper body swinging slightly towards the right)
This movement position if often seen while a troop of scouts is 'marching' down the sports field. In the ballroom it is often seen while a couple is dancing the slow fox-trot.

Sorry Mate, but that's CBM not CBMP. You can step outside parter in Tango without any swing.

Dear Phil.
Reviewing this post and tried what you said today. you pointed out the problem may occur in CBM.
In 5 steps of Tango, I got hang of it on 2-3 to wait for his body weight change, the problem resulted from (1)stopping use of standing leg and past my right foot without relation to left foot ( bad habit),
(my left knee should be roll continuously forward until I almost kneel then releas my right foot together with right side leg top (leaving the right hip behind) passing left foot ) or(2) my poist and head do not work outward enough with compact contact with my coach (sometimes I omitted it.) 3. I am not sure if I misunderstood, I am active in 5 step. if my standing foot work well, I have right timing , my coach will not strain his ankle due to my fault.
I am interesting in "softening" which I am not always keep it in my mind . Try reverse turn as you prescribed how an advance dancer do, I feel better. I call it : preplaning.
" CBM is inevitable if the turning action is to be continuous throughout the trun." I still can't catch it. maybe later I will. Thanks.

I noted that the CBM in a series of basic foxtrot ,V waltz ... body rotation slightly advances to the moving leg is very common. Is my understanding correct?

In foxtrot, waltz, etc, yes the body rotation known as CBM is slightly in advance of the moving leg, in effect, the body "leads" the leg and thus places the moving foot along the path the weight is taking, which is to say the moving foot lands at least partially overlapping the track of the standing one.

Or perhaps we should say the standing leg sends the body, and the body leads the moving leg?

Some who teach this CBM for the W,T,Q prefer to teach the Viennese Waltz differently , with the leg and body turning together. This seems to be supported in the way VW figures commence from an underturned alignment of not only the body, but underturned feet as well.