[cousin_it]

I think both versions are kinda lacking in rhythm. Here's my attempt, certainly imperfect too:

If you make an effort to omit unnecessary words, your sentences will be easy for readers to understand without slowing down. It also reduces the chance that readers will get bored and quit.

I used to uncritically accept the idea that concision was the single important thing about writing. The problem is, if you only ever write in short sentences, you'll neglect the skill of writing longer sentences that flow. And if you're writing anything longer than a tweet, you really need that skill! Having a natural mix of long and short sentences leads to a less "stuttery" feeling, and has a kind of hypnotic effect pulling the reader into your text and making them feel at home.

[dctoedt]

Or even: Try deleting words, lest your reader feel bogged down and give up — but brevity must serve clarity, so a few extra words might be worthwhile.

[tartoran]

To avoid repeating the readers I would change to: “If you make an effort to omit unnecessary words, your sentences will be easy for readers to understand without slowing them down. It also reduces the chance that they will get bored and quit.”

[nicoburns]

I was taught in high school that I should alternate long and short sentences in order to keep writing interesting. It seems like a pretty good rule of thumb.