One that that has made me unsubscribe from several communities here is when they are just bot-lead reposts of the equivalent subreddit. This makes these communities on lemmy objectively worse than the reddit equivalent because there is not the population to interact with the sheer volume of posts, and it just becomes spam without engagement.
My decision is primarily based on if the concept of the book appeals to me, and general reviews, but reviews don't make or break the decision. If a book is for YA but sounds like an interesting concept, then I'll go for it!
Also in the sciences (I'm a geologist), Megagram is often used. Most recently I wrote a paper which included discussion about the amounts of Mercury in the atmosphere, and Mg was the unit used.
Thanks for that - I'm on mobile, so not entirely sure what went wrong!