Like I said "without having to switch modes".
Yes the modes help, and I use the heck out of them, but it's still not enough. Plus I might need to hit a button a single time from another mode, but need to stay in my current mode.
This means pressing a button to switch modes (actually in my case toggling my mode switch), then press the appropriate button, then switch back to the original mode. Then there's the whole "accidentally leaving it in the wrong mode" occasion too.
A lot more time consuming than a simple "hold shift button, press button" process.