Imagine you are asked to find every student in a highschool, then told to find the students inside classroom #123. Doesn't feel efficient does it?
Imagine now you are asked to find room #123, then told to find every student.
This is exactly how it is for jQuery and the DOM. Selecting by ID is super quick, and if you use an id to find an element first, then the next part of the search only has to happen on it's children, instead of the whole page!
This will increase your app 20 fold. Do it.