It's essentially non-intrusive, really. It:
- creates a table
- stores a clean version of your posts within in
- hijacks the loop when search queries occur
when it is first called, it echoes a series of lines, one to a post that gets indexed. this generates an error (headers already sent) when the indexing is complete; just this once. follow a random link and the error will never be seen again.
there are no implications in the way you deleted the plugin, beyond the fact it will still be 'actived' when you try the next version. at your option, drop the table wp_sem_nodes.
btw, could you be more specific on the errors? i would hate to leave this unsolved.