Hey there

I´m new here an first let me introduce myself short.
My name is Thorsten from germany and i´m 32. I train now since 2years with 2 breakes cause of an operation, no injured btw

So i would say i´m serious lifting since 1 year an a few month, and is love it

When i started to worke out i whey 125kg, now 90kg an my goal is to reach 85kg at 182cm.
All gains and fatloses come from changeing nutrition an the workout.
Inspired and mutivated trough Scooby, so i have to thanks many many times 
Now to my question...
I do Dumbbell Pullovers with a SZ Barbell, laying on the floor.
I saw that scooby and most others do them on a bench or something similar things but why?
I that better for gains oder better for prevent injures?
When i do them on the floor, my motion stops at that moment when the weights touching the floor and and it looks like same motion.
So pls could someone explain me?
Thx a lot and greetings from germany
Th