Absolutely, heed this. Nothing will make some people stop reading like the laziness (in my opinion) of incorrect spelling and grammar.
You're not always publishing in your (or someone else's) native tongue, but there are services (free and paid) and software (free and paid) for this.
I'm guessing, but English is probably not your first language.
Use something like Grammarly for free (or even Word or Libre for *nix), put all of your text into it and use the suggested grammar edits. The things I noticed were simple like capitalization, no spaces after punctation, some misused words.