One question posed to Google was how does RankBrain impact crawling on your web site. Does RankBrain determine how much Google will crawl your site, i.e. your site's crawl budget? The answer is no, not yet at least.
John Mueller said RankBrain has no play when it comes to crawl budget. He said this on Twitter:
@AntBogarin No, that currently doesn't affect crawling.— John Mueller (@JohnMu) March 16, 2016
That doesn't mean it won't one day in the future.
Crawl budget is determined a lot by PageRank, your site architecture and external links - and of course, if your site is search engine friendly. RankBrain - not a factor now in crawl budget.
Forum discussion at Twitter.