John Gill Commentary Exodus 29:34

"And if aught of the flesh of the consecration, or of the bread, remain unto the morning, then thou shalt burn the remainder with fire: it shall not be eaten, because it is holy." — Exodus 29:34 (ASV)

And if anything of the flesh of the consecrations, or of the
bread, remain until the morning
Being more than the priests could eat:

then you shall burn the remainder with fire ;
that it might not be used in a contemptuous manner, or abused to superstitious uses; the same orders with those respecting what was left of the passover: (Exodus 12:10) ,

it shall not be eaten, because it is holy ;
which is the reason before given why it should not be eaten by a stranger, and being kept until the next morning it was ordered to be burnt, that it might not then be eaten at all.

It was not to be given to a stranger, nor to be cast to dogs, because it had been devoted to sacred uses; and it seems as if it was not to be eaten by the priests themselves the next day, who were to live upon the daily provision made for them.