do you keep dvd's as backup when upgrade blurays

[y2jman]

whether its same unrated movie or single movie doesn't have bluray dvd combo

for an example say today i received unrated wild things bluray same thing dvd

or say got nightmare elm on street bluray boxset but still have 1999 dvd boxset since that has 2d glasses watch freddy's dead and that dvd game came with it

i guess what i'm saying is it necssary to have a backup same movie dvd just in case 1 day bluray disc doesn't work or should you just stick with a movie that is unrated 1 format not 2