For those of us who are older, the Roth option in our employer's retirement plan wasn't available during most or all of our working years. Conversions still make sense, as many are able to do rollover at a lower tax rate than when they were working. Going forward all gains are tax free and there are no RMD's.
If you're still working and have a Roth option by all means take it. I contributed significant amounts of after tax dollars to my 401K during my working years but my former company didn't offer a Roth 401K option until after I retired at the end of 2015.