I noticed that in many websites/apps like Messenger, WhatsApp, sending SMS on iPhones, Google Hangouts, etc. The user's sent messages appear on the right side.
I'm wondering why not place it one below the other just like Slack?
Is there any specific reason why do they follow this pattern?
For reference:
A few months ago I developed and designed a chat service. This was something I put a decent amount of thought in, and the result just ended up being that I felt having the defined left and right meant that it was a lot easier to navigate.
The clear definitions between who is sending what makes the users life a lot easier.
Another aspect is that it depends on what platform you're targeting. Slack and discord for instance were designed for monitor screens, so having left and right makes it really confusing to follow. Messenger or iMessage were designed for mobile screens and it just makes most sense having the clear definitions.
I hope that's useful. Think about the platform you're designing for and what your demographic is most used to. Another thing to think about is do you expect multiple people to be in the same chat?
Having the bubbles coming from opposite sides of the screen creates a sense of separation between the two actors in the interaction: the User and their Interlocutor. This helps the user feel a sense of dialog despite interacting with their chat partner in a virtual environment devoid of the usual physical cues that an interaction with another actor is taking place. Otherwise, the physical colocation of both sides of the dialog (the phone screen) could create confusion on the part of the user as to which actor is performing what action and, potentially, reduce the 'feeling' of interpersonal interaction.
It helps you feel like you're being 'sent' a message from 'somewhere else'.
Using the sides makes more sense than using the top and bottom because the bottom-up (or top-down; see Twitter) new message stream pattern is the most common (some would say natural) pattern for updating a chat log with a new message. Why the right side for the user and left for the other actor(s)? Probably someone chose that arrangement for an early example of this pattern (e.g., the SMS app on first iPhone had this feature at least as early as 2008) and everyone else just followed suit.
Think about the fact that you have to type out your message and hit "Send" before you actually see it show up in the conversation list. You don't really read your own replies in the conversation view.
But Slack offers the one below one thread view since it offers little more features than other providers, Which really make it easy for the user to follow up on topic at a time by providing a high visual priority.
The reason for visually differentiating the messages coming from different participants in the chat by background-color or alignment is obvious, it's easier to follow the conversation.
Why alignment is or is not a good fit for some apps depends on UX testing, in my opinion. SMS used to have a limit of allowed characters and Messenger, WhatsApp, Google Hangouts were promoted as alternative to SMS when the apps were launched. Slack is known as an app focused on work collaboration and the messages are usually longer, so right alignment would be harder.
