Colorado Rockies: making the case for free agent Carlos Santana

The simple answer to that question is that he is a versatile hitter. He would not be a prototypical lead off man considering he hit .231 in each 2014 and 2015 and .259 in each 2016 and 2017 (he may not even lead off with Charlie Blackmon doing so well in the leadoff spot in 2017) but there is a reason why he lead off so often: his on-base percentage.
Carlos Santana has never had an on-base percentage lower than .351 in his career. Since 2012, his average on-base percentage is .365. This is because he walks a ton. In the past four years, his walk numbers have dropped a few each year but he still had 88 walks in 2017 compared to just 94 strikeouts. In the past four seasons, he has averaged 102 walks a season to 110 strikeouts. With that, this is why he has lead off so often.
But hitting fifth as well is a lot is no small task for a team that went to Game 7 of the World Series in 2016 and won 102 games last season. He has had between 79 and 87 RBI in the past four seasons. Also, he has had 19 or more home runs in each of the four seasons (including 34 homers in 2016). He will also hit his fair share of doubles (he hit 37 last season) which would play well in Coors Field.