Before I post this question, I searched in several places for answer for this. I really could not find the proper answer.
I evaluated the both way following...
$date = new DateTime()
amd
$date = new DateTime('NOW')
Is it must for the both above give the same result or is there any circumstance they both differ?
If you'll look into DateTime constructor definition you'll see that now is default value for initializing string:
public DateTime::__construct() ([ string $time = "now" [, DateTimeZone $timezone = NULL ]] )
That means both two calls above are always equal. If you'll not specify anything as initializing string, PHP will substitute now implicitly for you.