I strongly suggest you do some extensive reading on the advantages having a reference "blacker than black" area next to the screen can provide as far as improving the eye/brain's perception of just how black the blacks are within an image.
If you have no clue as to what I'm referring to, then I suggest that reading lesson all the more adamantly.
Referencing your one statement, yes, Black screen Trim can and historically has served as a mask for light overspill. But also historically, it's always been well documented and discussed extensively how the presence of a reference Black is "another" advantage such trim brings to the table. Bone up...so you know wherein you speak. Singh007,
Several recent Mfg Screen iterations utilize a diminutive Black screen trim to create a "Zero Edge" effect (...none of which are obviously"Zero Edge" if there is in fact a Black Trim...) and one must note that such Trim is in fact...Black.
In DIY circles, people have been creating "Floating Screens" that have NO
trim that were suspended out from a wall, and set against a Black Wall, (Paint - Velvet - Felt Cloth - etc.) to effect a unique look. So "Zero Edge" Mfg Screens are simply "Johnny come late to the Party" kinda thinking....essentially a sales gimmick. But a gimmick that in fact appeals to the esthetic sense.
And in fact, as the Contrast performance of PJs steadily improves, the need for having Black Trim is lessened. But NOT
eliminated. Should there be any ambient light present in the room that works to wash out Blacks on-screen to "any" degree, the reference Black Trim can help mitigate that effect to at least an extent commensurate to the degree of ambient light interference. However, past a certain point, it matters very little.
Which brings us back to why a Mfg Zero Edge Screen with teeny trim can even be considered. All the Mfg Screens that use them do so because they are mated with screen surfaces that try to boost the perception of having Deeper blacks through improved Contrast as a result of the screen being very dark, as well as it rejecting side-oriented incoming light.
We can do that with advanced metallic based DIY Screen coatings...and even with simple Neutral Grays to a somewhat lessor extent.
In the end, some have opted to use very skinny Trim simply because they liked the look...notwithstanding any attempt to improve performance, having a light controlled room, or any other reason. If your Screen build and installation criteria can accommodate such...it is simply a personal choice.