Hi. In the naver.com's dictionary, the entry for the word "backpack" is this.
A
javascript:flink( is a
bag with straps
that go over your shoulders,
so that you can carry things
on your back when you are walking or climbing.
Would you say the comma before "so that" is placed to allow a breathing space, which otherwise would not be placed, but it is placed since the somewhat long dependent clause "that go over your shoulder" is making it hard for a reader to read it and what follows it without stopping to take a breath?
Also, would you say, in these cases, commas would be optional (depending whether the person wrote it thinks a breathing space is needed or not)?
1. Shortly afterwards (comma?) he came home to pack his bag.
2. With a new car (comma?) he came screeching.
3.Through his friend (comma?) he relayed the message that Sue had given him the other day.
4. With our growing enrollment (comma?) we were able to hire a new person.