There was (and maybe still is) a valid use for sockets.
The "was" was when LSI IC prices were high. There was just too much
invested in them to scrap them along with a defective board. This still
obtains with CPUs and memory in PCs. At one time, two-channel serial I/O
boards for PCs were shipped with one 8250 and one set of 1488/89s. The
positions for the second port were socketed. Before that, almost any LSI
IC was socketed, such were the economic realities.
The "is" is when a ROM needs to be socketed for the purpose of a field
upgrade, although flash is making this pretty much obsolete.
I can't think of any other reasons. Are there any?
Cheers,
Chuck