I've been mostly playing cash, but the main site I play on cash games were down for 2 weeks, and MTTs were working fine, so I did some MTT play and study recently. I used to play exclusively MTTs.
I have been studying preflop ranges using online GTO tools (GTO Wizard). Jason Koon is a player I really admire and have listened to all of his interviews. In a few, he has said something along the lines of "You just absolutely have to mix preflop. If you aren't, that's pretty much just bad. You just have hands that need to be in both ranges".
I've always used pure strategies for preflop ranges that are simplifications of GTO mixed ranges. Ignoring the SB, when I look at GTO preflop ranges, almost always all of the mixed combos have the same exact EV for both actions (ex hands that do some limping and some raising), or almost the same EV with a negligible difference. I'm trying to understand why we should, for example, mix limping and open raising in these spots where both actions have almost the same EV for all combos - rather than simplifying to just developing an open raising range and have no limps.
I play fairly soft games, and probably simplified strategies are fine and perform well, but trying to understand in a general sense why we want to mix pre and randomize. I don't mind doing the work to understand why, but wondering if anyone can point me toward how I can learn this and understand the benefit. I could see if the solver had some hands it did one action with pure, and others it did another action with pure, and others that mix the two actions, then we want to mix to maintain balanced ranges and use the pure strats with the hands that want to. But when ALL hands are mixing, and the EVs of each action are the same for all hands.... why?