To extract a single file from the middle of a solid block, 7-Zip must decode all the data preceding it in that block, which can make extracting individual files slower.
Because 7-Zip can find patterns across different files rather than just within a single one, solid archives are usually much smaller than non-solid ones. A67zip
Updating or adding a new file to an existing solid archive can be slower because the software may need to recompress a portion or all of the solid block. To extract a single file from the middle