You're not alone I was told the same many years ago ..
Truth is , I believe it to be completely incorrect advice , in hindsight .
It's not even possible to feed my 7' Snow Boa , or the Burm or even the Retic in a separate viv THEN move them afterwards ... Also I defy anyone to come and feed my collection of King snakes in separate rubs then try and get them in their own vivs
I feed all mine in-viv now and simply place two of three little pieces of card (or cardboard if it's easier ) on the floor of each viv .
Never , ever , had any issues .