If you increase your English proficiency, you often will be able to get a new job, a better job or a promotion where you are working. Having English speaking clients is very attractive and often a necessity for millions of businesses worldwide. You may even get a higher salary or paid more hourly for speaking English fluently.
Often if an employer (a business), is having trouble deciding between two potential job candidates; they often choose (or hire) the candidate that speaks proficient English rather than the one that does not.