Why use the "last seen" feature?

Question

Stack Exchange websites have a feature called "Last seen some time ago".

What is the real purpose of this? And why do social networks like Google+ or Facebook don’t have it? And what are the pros and cons of having / not having that option?

Answer 1

The 'Last seen' feature can be useful in a handful of situations.

Mediating communication

Some IM media like Facebook Messenger or Google+ Hangouts can be used both as synchronous media or asynchronous.

Knowing that a person is currently offline allows you to understand that they may not be able to reply to you. If you need an immediate answer, you may then switch to more direct means of communication like phone calls or in-person chat.

Even in the middle of an ongoing synchronous conversation, knowing that the person is no longer offline might help you understand that they are currently experiencing connectivity issues and are not actively ignoring you. This might ease situations where people might otherwise get offended, e.g. in professional contexts.

The downside is that such a feature is privacy-invasive: it can help reveal to someone where you are or what you are doing, and tell them that you are ignoring their messages indeed. This is relevant on social networks and most specifically on dating apps. That's why most IM apps will allow you to turn off 'Last seen' for specific users or for all users. For instance, WhatsApp will not display a status indicator, and so the other user will be aware that you do not wish to be tracked. Likewise, Tinder no longer tells you whether your matches have been recently online or not.

Indicating that a user is active

On apps like Wikipedia, StackExchange, AirBnB, CouchSurfing or other community websites whose content is produced and curated by users, it is sometimes very helpful to know that a user is active. You then know that they will quickly respond to a request or comment sent within the apps. If they have been inactive for a while, you may instead want to find another means of communication to reach them, or restrain from engaging with them altogether.

There is a somewhat different privacy concern here: you are not expected to continuously engage with a specific community member (therefore, you don't have to hide from inquisitive members), but your continuous activity on a platform might be an indicator of how you use your free time or work time. Some employers may dislike that one of their staff members spends time on a community website and might use the 'Last seen' feature as a means of gathering evidence that the employee engages on online social media during work hours.

Answer 2

Last Seen is used to show how active this person is, in sites like Stack Exchange it makes sense, if im browsing a user account its usually in order to have an insight of how active this user is, and/or whether the user is reliable or not.

For social networks if you dont see when was i last online i am likely to be more active.

In Social Networks it will help Active users to interact more, while it will help Inactive users to interact less.

If you want to send a message to someone, then you see this person logged in last time 6 months ago then you might not do it.

While you will be more likely sending it to someone who was online last night.

However if you send that message to the person who logged in 6 months ago, then at some point he sees the message, he is likely to log in more than before because the interaction is increasing.