It usually speeds up basically everything parallelizable that looks kind of like a parser, lexer, tokenizer, .... Unless somebody goes out of their way to design a format with fewer data dependencies, those workloads are crippled on modern CPUs. That includes (de)compression routines, compilers, protobuf parsing, ....

The only real constraint is that you can actually leverage multiple threads. For protos as an example, that requires a modified version of the format with checkpoints or similar (which nobody does) or having many to work on concurrently (very common in webservers or whatever).