I was deleting Wine by using rm -rf on it's directorys (yeah, it's a bad way to do it) and I prematurly hit enter on the command "rm -rf /usr/local/include". So my question is how important is that directory, and should I reformat or what?

On my laptop, my /usr/local/include is empty, so you just need to create is again hopefully.

Oh, thats good. Hopefully I'm overreacting, but still, what is /usr/local/include used for? Thank you!

The FHS says:

"The /usr/local hierarchy is for use by the system administrator when installing software locally. It needs to be safe from being overwritten when the system software is updated. It may be used for programs and data that are shareable among a group of hosts, but not found in /usr."

The /usr/local/ directory is similar in structure to the /usr/ directory.
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If you install programs yourself in the /usr/local directory, the program file will install header files in /usr/local/include.

Why a possibly shared directory would be called local I don't know. It was a subject I brought up myself.

Weird, thank you for digging that up.

That depends on the definitions of "remote" and "local". For instance, multiple machines within the same room can mount the same /usr/local directory from a nearby network server.