Solid archiving significantly increases compression, especially when adding a large number of small, similar files.
But it also has a few important disadvantages:
slower updating of existing solid archives (you have to repack all the files);
to extract a single file from a solid archive all preceding files must be analyzed. This makes extraction from the middle of a solid archive slower than extraction from a normal archive, but, if all files are to be extracted from a solid archive, the extraction speed will not be affected.
if any file in a solid archive is damaged, it will be impossible to extract all files which follow the damaged area.
