In SC2 I generalized I had 3 characters. Ivy main, 2nd Astaroth, 3rd Yoshi.
Ivy I knew well, but if they could beat her I brought out Astaroth and usually could beat them. If both lost I'd rely on the awkwardness and life gaining power of Yoshi.
However in SC4 my Ivy is VASTLY better than my Astaroth and Yoshi. They've pretty much become novelty acts whenever I feel like having fun rather than owning competitively with Ivy. At this point I'm so specialized in Ivy I can't find a single character to adopt as a true secondary. No character operates like her and being so used to her complexity I feel awkward playing the simpler characters. I've tried Astaroth, Yoshi, Amy, Nightmare, Cervantes, and Algol and I simply can't adopt any of them beyond spamming the basics, Astaroth being me most intelligently played of them all.
I fear generalization in 4 since each character is so vastly different than past installments. If I were to say pick up Hilde (who I would love to but have no clue how), she may harm my Ivy since they're are a full 180 on tactics and I may get them crossed. I still find myself trying to do Ivy's 2K with Nightmare for a quick low and doing nightmare's slow footstomp instead. Ivy needs very fast inputs that are deep and complex while Hilde needs constant focus on holding and releasing buttons and even requires me to remap my controller possibly.
The only real advantage is when it comes to counter pick I guess. I'm trying to adopt a fast character to compete with rushing characters that are difficult for Ivy. I need to try Talim and Taki next. I don't like the JF's of Setsuka. However, it may just be better to learn counter strategy with one character. Comfort will be out frame data.