It can be quite useful to still access and use the element picker for a web site which has been whitelisted, as the element picker allows the creation of more specific filters, narrowly targeted at the current web site, thus the filters created through the element picker are more efficient, especially concerning cosmetic filtering.
A user may want to improve the efficiency of cosmetic filtering on a specific web site (because say, the ads "flickers" briefly), and thus would disable uBlock to let the ads appears, use the element picker to create a very specific cosmetic filter, then re-enabled uBlock with the new, more specific filter which works better than generic ones.
It can be quite useful to still access and use the element picker for a web site which has been whitelisted, as the element picker allows the creation of more specific filters, narrowly targeted at the current web site, thus the filters created through the element picker are more efficient, especially concerning cosmetic filtering.
A user may want to improve the efficiency of cosmetic filtering on a specific web site (because say, the ads "flickers" briefly), and thus would disable uBlock to let the ads appears, use the element picker to create a very specific cosmetic filter, then re-enabled uBlock with the new, more specific filter which works better than generic ones.