In simple terms, bots join and harvest data, some are 'good' - google, yahoo etc others less so. Spammers are fake accounts eg ddelorischandleri who joined this week. I picked up on it and deleted the account. asking a couple of questions will make it easier for me to either approve or delete membership, and i doubt they will be able to answer the preferred scale question.
Dormant accounts (no post) are different, and if they are genuine people then I leave them. fortunately being a small forum none of this is too much of a problem.