For example, tables in relational databases like sqlite are representationally isomorphic to tabular files like the output from `ls -al`. Sqlite has a lot of useful performance optimizations (including eg, not having to encode strings as "\x20" or the like if you want arbitrary bytes), but those come at the cost of a data format that you can't easily (not even notice that you needed to and did) reverse engineer, when either writing new software to consume or emit it, or even just visually inspecting it in a editor that doesn't already speak that format.
For example, tables in relational databases like sqlite are representationally isomorphic to tabular files like the output from `ls -al`. Sqlite has a lot of useful performance optimizations (including eg, not having to encode strings as "\x20" or the like if you want arbitrary bytes), but those come at the cost of a data format that you can't easily (not even notice that you needed to and did) reverse engineer, when either writing new software to consume or emit it, or even just visually inspecting it in a editor that doesn't already speak that format.