One row per post (default) gives every post its own row, with the full account record repeated on each — the shape to pipe into a warehouse, and what existing code reading this Actor expects. One row per account gives each account a single row: the profile at the top level (handle, name, bio, follower and following counts, profile picture and banner, website, location, verification and badges), and its latest posts under posts with all 26 of these fields — id, type, url, twitterUrl, text, createdAtIso, timestamp, likeCount, retweetCount, replyCount, quoteCount, bookmarkCount, viewCount, isReply, isRetweet, isQuote, isPinned, isSensitive, lang, hashtags, mentions, urls, media (the pictures and video, so you do not need the other format for them), imageCount, videoCount and authorUserName. Same price either way; the row is a fraction of the size, and it is the one to pick when you want an account's details rather than a stream of posts — or when you are checking a list of accounts: each row also carries latestPostAt, daysSinceLatestPost and timelineWithheld, and an account that is suspended, deleted or protected is a row saying so.