Do we need either?

What is the difference between "You can have an apple or an orange" and "You can have either an apple or an orange". Why do we need the word either?

To set the content - this is for a technical manual. American English. A more representative sentence is:

"The menu allows you to choose a large font or a small font" vs "The menu allows you to choose either a large font or a small font"

The second version sounds like a final suggestion (choice of two), excluding other possibilities (prevents from understanding 'or maybe some other fruit').

P.S. I think you don't need 'either' for your menu, it wouldn't add useful information.

In a phrase either P or Q, where P is long and complicated, it is helpful to put either in there to clue the hearer in as to where it starts.

It is similar in both P and Q. We do not need both if P is short and simple, but it is useful when P is complex.

Thirdly, in neither P nor Q I recommend always using neither.