javascript - Using jQuery object understanding

I had to jump into jQuery development without getting too much time into learning all the associated basics, so there is one thing that throws me off quite a bit.

I see two different ways our developers access jQuery objects:

Case 1:

var container =  $("#containerId");

// Then use it as:
container.hide();

Case 2:

var container =  $("#containerId");


// Then use it as:
$(container).hide();

From my thin up to date knowledge, by wrapping a container as in var obj = $(container), we get a jQuery object obj that we can further work with.

But then why do I see intermittently developers wrapping it again when using as in $(obj).doSomething()?

Edit: the question suggested as duplicate is asking about best practices and although similar, my question is purely on understanding of jQuery object wrapping.

Answer

Second wrapping does nothing as I remember. So if there can be a selector a dom element or a jQuery object you can just wrap it and do not care about what it was.

But if you know it is a jquery object, you shouldn't use wrapping.