A Talent Acquisition leader in an industry with a high turnover rater has recently reminded me: when you need to fill a job, make sure to look inside, first.
Indeed, internal mobility should be expected to fill at least ⅓ of your open positions. Not only that, but it has a double benefit: it will increase your retention rate and fill your much-needed, typically higher-level role. Yes, you may need to backfill, but it's good to keep that obvious source in mind.
Another leader shared with me a simple, yet very effective way to boost internal mobility: to have each internal candidate receive a call from your recruiter, within 48 hours of their application.