What is the reason for "stretched" letters in the Torah?

Question

I noticed that in many Sifrei Torah, Sofrim prefer to "stretch" certain letters. It seems that these letters are stretched to end a line if there wouldn't be enough space to start a new word. That's not always the case, though; sometimes these letters appear in the middle of a row. Some sofrim use this technique often, while others don't use this at all.

Is there a reason for stretching the letter other than what I just mentioned? Is it some "artistic" form? Are there limits to either which letters are allowed to be stretched and how much stretching is allowed?

Note: I am not asking about large (rabbati) or small (ze'ira) letters. This has been addressed in a few other questions. I am talking about the horizontal size.

Answer 1

Pasted from my answer to this question:

Stretching letters is not a matter of custom, but one of practicality. Halacha requires the columns be justified. Microsoft Word handles justifies text by widening spaces between words and letters. You can't do this in a sefer torah, so the sofer stretches letters instead. Good tikkunim minimize the number of "short" lines that require stretched letters, and good sofrim regulate their ksav so that the stretching is less noticeable.
While some people (myself among them) think that stretched letters add something aesthetic to the calligraphy, Halacha considers stretched and cramped writing a lower quality ksav.

Some sofrim will prefer to stretch a letter in the middle of a line instead of the end so it looks more artistic and less like they're filling up space. (Personal experience covering up bad planning.)

Answer 2

One is prohibited from stretching letters that will look like other letters, or otherwise cease to look like themselves, if stretched.

The easiest example is that if you stretch a vav, it becomes a reish. A stretched zayin becomes a daled. If you stretch a yud, it looks weird, so you can't stretch it. I'd think a stretched aleph would also look weird, but might be recognizeable. A regular chaf can be stretched, but a final chaf may not (it will look like a large reish). Neither regular nor final nun can be stretched. Some other letters would look weird but recognizeable if stretched.

Letters like bet, final mem and samach which require stretching two lines tend to provide a less pleasant asthetic, so the preference is to stretch something else, but they can be stretched.

Answer 3

There are several reasons for this, of which I have heard two:

1. Left justification as in @Yitzchak's answer above;
2. Emphasizing the poetic character of certain sections