Farid

im new here ,please take it easy on me!
i want to know what is common procedure for thrust on final approach,i saw many many videos (world air tours,pilot eyes,...)
some pilots stay on A/THR active on final approach _speed managed mode)when touching down going back all the way on the thrust to idle then automatically A/THR get disabled...after that reverse and finish...
many other for example at 2~4 DME from TDZE ,going back on idle trust so A/THR get disabled again automatically ,while stay on speed managed mode,and after that reverse and so on...
i want to know first ,am i right in figured out this 2 ways i said?

which one is common by pilots?

and why some pilot choice A/THR off for approach ?!i mean A/THR on have not any bad effect any way,why they cut that off?

if some body knows about that systems ,let me know
thank you in advanced