There are so many different situations...
For instance, you have just made G/S interception at 3,000 and are waiting as usual to the flaps 2 moment, but then captain puts his hand on the lever. Then you think "OK, I got it, but why so soon?" then call for flaps 2. Then you see the TCAS traffic ahead, which is now getting closer than 5 nm. "So that's why!" Thank you captain.
And other times he puts the hand on the lever just because he would do it in that moment and he wants you to do it exactly at the moment he would do it. Well, it is annoying sometimes, makes you feel "accused".
In take off, some captains consider autoflap retraction as an offence. Others like to make use of it. By the way: Anything written regarding this?