You can pick up readers who only usually read on Kobo or Nook, who may be enticed over to Amazon to buy the other books in the series in print format. (authorunlimited.com)
Readers tried the freebie and went on to buy other books in the series. (lindsayburoker.com)
When readers download a free book and like it, they tend to buy other books in the series. (angiesdiary.com)