After Roger's death, he was considered the top dog of the seas until his own death. Due to his indifference towards high-sounding goals (he already achieved his dream by having a family), the world maintained a certain stability. His death marked the rise of Blackbeard, who took his former captain's territories (which he knew inside out, so his own intel of the WB Pirates helped him a lot), and allowed Kaido and Big Mom to further their own agendas (WB was a "barrier" for their goals; if Newgate didn't exist, there would be probably only two emperors — the worst two out of the og Yonko — and the New World would be even more chaotic).
I guess that he indirectly helped the "mid generation" (e.g.: the Red Hair Pirates, the Sun Pirates, Dragon, Mihawk, et al.) to grow, thus being a key figure to Luffy's own development, as he was motivated to go out to the seas by Shanks.