What It Does For The Player
First and foremost, Keith requested the trade. As he nears the end of his career, he wanted to be closer to family, who reside in Western Canada (Vancouver). During the COVID-19 pandemic, with travel restrictions, a condensed schedule, and health risks involved, he did not get to see his family much. After 16 years in the Blackhawks organization, Keith earned the right to make this request, and the Hawks had every reason to try and accommodate the request.
Keith, playing for the Oilers, should be able to travel much more freely throughout Canada, and should be able to spend more time with his family.
Secondly, Duncan Keith has averaged nearly 25 minutes per game of ice time over his career. That takes a brutal toll on the body, even for someone as fanatical in his training and conditioning as Keith. As a soon-to-be 38-year-old defenseman with nearly 1200 regular-season games under his belt (plus an additional 135 playoff games), he would be well-served to reduce his minutes to improve his effectiveness.
The ‘Hawks were going to lean heavily on Keith regardless of the rest of the D-corps, so he could have expected 23-25 minutes of ice time per night for the remainder of his contract, which in my opinion has led to declining performance for Keith over the last few years. Playing behind Darnell Nurse, nearly 12 years younger than Keith, should offer him the chance to lower his average ice time a bit, which should keep him fresher throughout the season.
It also gives him a chance to be more effective on special teams, because he will not be counted on as heavily in 5 on 5 time. Keith is a skilled puck-mover and can be an effective Power Play QB on the second unit, as long as his minutes are controlled, and he is not overworked.
Finally, a fresh start is sometimes the kick a player needs to revive their excitement for the game, and their desire to put in the work and effort. While this has never been an issue for Keith, imagine lining up and seeing the likes of Connor McDavid and Leon Draisaitl playing in front of you, and knowing that you have the firepower to be in every game all season long. That has to be a morale booster to Keith, even after playing with Toews and Kane for the last decade.