I'll make Another comment here. This thread is in the Kenpo forum and this is a debate among the Kenpo folks for a long time. The Parker-derived lineages tend to structure their curriculum in a way that is somewhat different from how many other systems do it. They have lists of "self defense techniques" that are kinda like little bunkais in that they give a sequence to practice a defense against a specific attack. These are stand-alone techniques, and the belt curriculum and ranking promotions tend to be based on learning them. And there are a lot of them. The lineages closest to Mr. Parker at his death tend to haves total of 150 or so. The lineage in which I trained is Tracy, we had a total of some 380, plus many variations. Some lineages have more, some are streamlining and have fewer.
Personally, I found this approach to a curriculum to be very cumbersome and for me, not useful or functional. That is why I no longer train Kenpo. Other people feel it works. To each his own.
However, this debate makes more sense in the Kenpo context because it is about practicing these hundreds of self-defense combos on both sides. When you've got a list that goes on forever, adding the other side does add to the workload and the time needed, tremendously.
For this debate, context does matter. And yes, when I did train Kenpo, I did practice both sides. I did it from day one and was shocked to discover others were not doing the same.