An MQL (marketing-qualified lead) has shown enough interest, through downloads, visits, or form fills, to be worth marketing's attention. An SQL (sales-qualified lead) has been vetted as ready for a sales conversation.
The handoff between MQL and SQL is where many leads get dropped, because the criteria are fuzzy and the data is incomplete.
When every interaction is captured automatically, the MQL-to-SQL handoff is based on real signal instead of guesswork.