Most plugins work in multisite with no changes. The main exception is if you want your plugin to have different settings or behavior available network-wide vs. for individual sites — if you look closely at the example you pointed to, it has two separate settings pages, one for the whole network, and another to allow individual sites to override the network default.
Well i looked into the code but i am not that experienced to get that fast what it really does, so its just to setup defaults for the network, meaning if i remove that code it still works but every site start at the defaults hardcoded inside the plugin right.
You’d have to try it out to know that. But it’s generally a poor idea to edit a plugin just because you don’t plan to use those settings – aside from the possibility of breaking it, you’ll certainly lose all your changes the next time it’s updated.