It could be useful if there was a C program you would like to run, but the only tool available was Excel. Maybe strict IT admins had disabled the ability to run anything but Office, and even VBA macros were disabled. Although in that scenario it would be better if the compiler was written in C and could bootstrap itself.
I don't mean to put down OP but isn't it kinda straight forward since assembly is just a 1:1 correspondence with machine instructions? simply pasting the assembly program into a column then looking up each mnemonic in an association table linking each mnemonic with it's machine representation and writing the result into a new column would work. The Labels->Addresses mapping is another lookup but over the program column itself, looking up the row where the label is defined and using that as the offset from the start address of the program. An assembler is just a fancy string processor, Excel is mighty good at string processing.
What I would bet a respectable sum on is that you can't parse/process/interpret even the simplest recursive languages (e.g. arithemtic, Expr ::= Expr + Expr | NUMBER) from pure Excel. Forget expressing the algorithm, there isn't even a suitable data structure to iterate over.
Here is a video of a doom-alike in excel, explained by someone with a bird on his head. He's not clippy, but a real person with a bird on his head. [1]
Here is a video displaying a walk-through of the Excel easter egg that showed the Hall of Tortured Souls! [2]
Excel 98 had an Easter egg which was like Magic Carpet! If I recall correctly, you fly over a twisted purple and orange landscape while an obelisk emits the credits.
95 had the “Hall of Tortured Souls”—a 2.5D first-person walker—which was more Doomlike.
