To clarify slightly, It is ideal to have your GPU fully utilized, but NOT for it to be overloaded when playing a game where the GPU is utilized strongly. 80-100% utilization is wonderful, it means your GPU is performing the tasks you're asking of it to the fullest of it's ability without being overloaded.
However if your GPU is hardlining 100% constantly at all times, and you're getting stutters, framreate dips, and inconsistent performance, then your GPU is overloaded- too much is being asked and it can't keep up.
Now, you don't exactly want a game to be using your GPU for no good reason- Something like Heroes of Hammerwatch using 100% gpu is just excessive. But if a game warrants and can utilize that 90-100% range without doing it for no reason, then you want it to, because otherwise you have excess power just sitting there doing nothing.
Wanting less than 90-100% utilization when it's doing it's job would be like buying 32 gigs of RAM and only ever using 16 gigs of it. The RAM is there to be used- It's not doing anything for you unless you're using it; Or buying a super powerful CPU and only ever using it to run Windows' calculator.
TL;DR: You want full utilization, not bottleneck.
With regards to the Opening Post, 100% GPU at the menu screen would be abnormal- There's nothing happening there that warrants 100% gpu load. That you were also getting 100% in game with an abnormally low framerate as compared to what you were experiencing prior to that was also abnormal.