Mixing different grade of gasoline from one brand/station

Hello my fellow tsikot...

any chemical engineer specializing in fuel or someone in the fuel industry here?

for example i have a 42L gas tank, a toyota Vios 2NZ-FE engine,

upon 2nd low fuel warning (fast blink) i fill up Shell VPower NitroPlus RON95 @ 20L + Shell Fuel Save RON91 @ remaining capacity lets say 19~20L to make it a full tank

both grade of fuel from same gas station...

now, what are the advantage and disadvantage of doing this?