DaveR4470 wrote: As noted above, the only time you don't want to use the max level button is with Devil Dinosaur. DD "starts" each level with something like 20% of the needed ISO for the next level already credited. Also, I believe DD requires more ISO (on paper) to level than a regular 4*. I think the extra ISO is meant to level out DD's actual required ISO back to a normal 4* level. (Please note that I am completely talking out of my posterior here....) But the max level button does not take into account the extra ISO bonus per level. So you pay more by using the button than you do by individual leveling. Or something like that. tl;dr don't use the button with Dino. I don't think it matters with any other character.
Punisher5784 wrote: According to the devs back in 2015, they stated players feel it's "fun" to press the level button down.. so yeah just hold the button down to bring joy to your MPQ life!