When you apply for a job online, which is the main way to apply for a job now, then you will usually be asked to submit a CV. You might also be asked to provide a covering letter, which you shouldn’t see as an inconvenience, but instead as an opportunity to express your real interest in a job and to show why you stand out from the crowd.
You should definitely write a cover letter even if you don’t have to, showing that you are really passionate about the line of work and the industry. Sometimes, a recruiter will only look for candidates who are happy to provide a covering letter, showing their clients that the candidates they are finding are driven and enthusiastic. You don’t have to write a cover letter from scratch, just make sure that you have several templates available to mix and match your cover letters.