When applying for any job, it is absolutely necessary to make a good first impression the first time that you come into contact with a potential employer. Many people may automatically assume that the previous sentence refers to an interview but that is not the case. If you have been asked to send a resume in to apply for a specific job then it applies to your cover letter. The layout of your resume is of course important, but the cover letter is the first thing a potential employer will see.
Your cover letter should always be included with a resume and should most definitely aim to impress because it will be taken into account! Employers do not just throw away your cover letter and read the resume. Instead, they will take in everything you have to say on there. It is the first indication of what you are like as a person and whether you are a credible candidate or not. This is why you should always take the time to write your cover letter yourself and never use one of the many templates available out there.
The personal touch is absolutely essential when writing cover letters because every employer will be able to tell whether you have written them yourself or not. Using a template without editing it and tailoring it to suit you is incredibly dangerous. By all means look to templates for ideas and read up on what makes a successful cover letter, but make sure that you put a little of yourself in there in order to make it completely unique.