I run a very small browser game (~120 weekly users currently), and until I put its Wiki (utterly uninteresting to anyone who doesn't already play the game) behind a login-wall, the bots were causing massive amounts of spurious traffic. Due to some of the Wiki's data coming live from the game through external data feeds, the deluge of bots actually managed to crash the game several times, necessitating a restart of the MariaDB process.
The data transfer, on the other hand, could be substantial and costly. Is it known whether these crawlers do respect caching at all? Provide If-Modified-Since/If-None-Match or anything like that?
e.g. they'll take an entire sentence the user said and put it in quotes for no reason.
Thankfully search engines started ignoring quotes years ago, so it balances out...