Learn English – Difference between so called and called so

Does it make more sense if we insert that?

to divide something into many small parts especially so that you can use the result for your own purposes

If not, then let us consider one of the definitions of so.

so

19. in order that (often followed by that)

So we can reword the original into

to divide something into many small parts especially in order that you can use the result for your own purposes

Apparently you (OP) think that a comma would make sense "when spoken", but I personally didn't think it made a difference. This is because, typically, in the usual dictionary writing style, the word especially refers to the text the proceeds it, not precedes it.

I think there are a number of things that are strange with this entry. Two that I can formulate are 1. The entry goes from writing in the infinitive style (I don't know the correct name) to dropping the infinitive style and addressing the reader. 2. The entry drops the "that" in "so that".

Dictionary entries not usually address the reader. So that was odd. I also think "so that" sounds better, per se. Not because it is any more correct, but simply out of habit.

Maybe the learner dictionaries are different, or this particular entry is an odd, but I might have written it as

1. to divide something into many small parts especially to use the result for one's own purposes
2. to divide something into many small parts especially for one's own purposes

To paraphrase "Pirates of the Caribbean", think of this more as a guideline than an actual rule. With creative writing, it is often possible to place the adverb anywhere it sounds good.

Because this is an uncommon placement, when done properly, it can sound dramatic.

They flung wide the doors of the hall, letting sunlight stream into every dark corner.

Done poorly, or in an odd context, it just sounds awkward, e.g. "She ate greedily the cake."

In the future, if you see this kind of sentence structure (and you trust the writer is doing it on purpose) take note of the context, and recognize that the sentence might feel different from the usual phrasing.