I checked my 2 Bitcoin Core installations (on different systems): The size of blocks is 510671104 and 509643300 kB (the difference is 1027804 kB). The oldest installation is the largest: it makes sense the more recent installation skipped all old orphaned blocks.
if it's useless, can we delete it manually on the block file?.
is it dangerous if I edit manually (delete) blocks (that almost 7K file)?
what is different blk and rev? (.dat) inside block folder