The use of "BY"

[tonyp]

Hi can you help please professor,
Can you tell me why the word by is used in the following sentence when it isn´t needed.
I save money by doing my own cooking

[JJM Ballantyne]

No, I can't. It's language not mathematics we're studying here.

In English, you have the choice:

I save money by doing my own cooking

I save money doing my own cooking

There's some stylistic ellipsis going on here, that's all.

[Roro]

Hello JJM Ballantyne
I'm with you. I'd like to study language, too.

[Casiopea]

Welcome.

I save money by doing my own cooking

Additionally, there is a method to the mathness. Call it "efficiency".

Both the preposition "by" and the adverb of means "doing my own cooking" express a means. The former expresses it in a word, whereas the latter expresses it in its function. "by" is redundant. The meaning it expresses is already housed within its object's structural function.

EX: I saved money. How/By what means? By doing my own cooking.
EX: I saved money. How/By what means? Doing my own cooking.

With or without "by", the phrase "(by) doing my own cooking" functions as an adverb of means, which makes "by" superfluous in context.