As a Roblox Developer and Game Designer, it is incredibly hard to make some professional game design decisions that are consistent with all players.
The camera is one of the most important aspects of a game, and games need to be designed accordingly to it. Roblox will always fill it’s screen as much as it can on any device and window size, thus making some game design decisions that revolve around the camera either incredibly difficult to make or inconsistent with the players playing your game.
This reason is one of the few reasons Roblox developers have less freedom in game design over normal game developers. People who make games outside of Roblox typically always have one set aspect ratio, or multiple exact aspect ratios to work from that they selected.
All Roblox would need is an option, inactive on default of course, for game developers to restrict screen size and aspect ratios to a certain value or values for their game.
A feature like this would allow much more freedom in polishing game design for game developers of many genera, especially ones that would require precise movements or visual ques.
For example, it is incredibly difficult to make a polished side-scrolling platformer game on Roblox. Those types of games heavily require the knowledge of what the player can or cannot see to construct it’s game design. A user with a wider or tighter screen than initially perceived could cause problems with the game’s design and lessen the experience.
If this issue were addressed, all players would have a similar and 100% intentionally designed experience, with no distinct advantages and disadvantages that could hinder a user or other user’s experience with a game.
I do understand that Roblox Studio has an option to view the screen in various screen sizes and aspect ratios for different devices, and this does help a lot. However, with the exception of the Xbox One, it is impossible to restrict one of these aspect ratios if they don’t fit or work with your game without disabling the entire platform. It would be much easier and less tedious for the developer of a game to set specific aspect ratios that fit the best they can into a screen instead of having to develop for 15 different screen sizes just so mobile users have the same experience. This also does not help the large variety of screen sizes and aspect ratios PCs can use.