Archer, who will turn 25 in August, was a third-round pick (No. 97 overall) of the Pittsburgh Steelers in the 2014 NFL Draft. The Kent State product was picked that early because of his blazing speed; his 4.26-second 40-yard dash time at the Combine is the second-fastest in the event's history, and helped him rise up draft boards despite his sub-5'8", 173-pound frame. He also happened to be highly productive in college, finishing his four-year career with 3,536 yards from scrimmage on 424 touches with 36 touchdowns, plus another 1,444 return yards (mostly on kick returns) with another four scores. He averaged 28.2 yards per kick return in his career.
In Pittsburgh, however, Archer did not pan out. He appeared in just 20 total games between the 2014 and 2015 seasons, touching the ball just 20 times on offense (for just 63 yards) and logging a combined 24 kick and punt returns, before the Steelers waived him last November. He signed with the Jets on a reserve/future deal this past January, but did not last there past spring workouts.
Archer averaged 25.3 yards on 14 kick returns last season, which would have felt like a breath of fresh air on Buffalo's awful return unit last season (their own leader, Walter Powell, averaged 25.7 yards on just three returns, which happened over the final two games of the year). He'll at least have an opportunity to make waves there - and if the team can settle him into a defined position on offense, his speed would be an obvious asset. But considering Archer's career trajectory, that currently seems like a long shot.
The Bills had an open spot on their roster - they're allowed to carry 90, and were under that threshold - so they do not need to release anyone to make room for Archer on the roster.