What's the different of ( -name=>value ) and ( name=>value )

[Panda-X]

I have a script like this :

sub This { print @_ }

This ( -x => 100 ) ; # prints -x100
This ( x => 100 ) ; # prints x100

##
It seems that's something just as is.
However, I saw many packages would like to use :   -option => value
So what's the point for this style ? Is there any specific reason for that ?

Thanks,
Panda-X