The point of reading from the bottom up is largely for sight-reading as a collaborative pianist or, perhaps, ballet class.
The essence of music is the bass and everything builds on that so get that down first and keep the tempo and the rhythm going. The right hand can be reduced to simple chords or melody and generally isn't as important, in that work, as bass.
If you're reading on your own to learn or discover new music or just enjoying reading, it matters not; just keep all the buffers filled before committing to playing.
I typically read from the bottom up as I sometimes have to keep the foundation of the music going for others and when the reading gets tricky the left hand may be all I get time for.