Here is your fine-tooth comb! You'll need it to go over your writing!
Proofreading is the process of reviewing an essay or other piece of writing with the intention of catching any misspelled, misused, or missing words; incomplete sentences; typographical errors (typos); and any punctuation, grammatical, or mechanical errors that spelling and grammar checks may have missed (or incorrectly changed). Proofreading is that final process of checking over the essay after the ideas have been developed and revised (during the editing process).
Hopefully, you—as the writer—have worked hard to form and develop your ideas. Now it’s time to put the same amount of work towards polishing those ideas.
How many mechanics would build a car from scratch just to leave it unpainted or unpolished?
Can one or two misspelled words or comma splices really make that big of a difference?
In a word: YES!
Think of it this way, the more obvious the mistake the more likely a reader is to notice it. Typos and the like can lead a reader to rethink the credibility of the writer: “If they didn’t bother to check their work before showing it to their audience, who is to say whether they checked out their sources or did any background research on the topic?” If you were careful and attentive during the writing process, the last thing you’ll want is an audience that thinks you’ve been careless and negligent.