Selecting a Very Poor avatar with Impostors isn't possible in-app, despite them working fine when bypassed. Since you and others will be seeing the Impostor, and those with performance settings set to allow Very Poor still seeing the high quality, there is not too much of a reason to disable this

edit: similar to https://feedback.vrchat.com/mobile-alpha/p/avatar-only-able-to-use-quest-avatar-even-if-impostor-available