It can be tempting to quit your job without having something else lined up, especially if you are in a difficult position at work, you might be being discriminated against, suffering from stress or the role maybe completely different to what you thought. Sometimes when you take up a new position you don't realise what you have let yourself in for and before you know it you are in too deep.
For various reasons, this can be a hard decision to make but from a future employment and job application point of view, it's definitely worth sticking it out and job hunting before you make the big decision to jump ship.
Statistics show that you will be more likely to be shortlisted and find new employment faster when already employed elsewhere than if you are unemployed.
Employers are more interested in applicants/job seekers who are currently employed. This is because they see this as you are good enough at your job that somebody else is willing to pay you to do it. Also, it makes you look committed to your job - if you were to quit before you apply for new positions you might look like you have no commitment to your employer.
Being employed also makes things easier for yourself when going to interviews for future employment because if you are unemployed at the time of the interview the employer is most certainly going to be asking the question "why?". Definitely something that is not easy to answer if you have quit your job under negative pretences.
Try to maintain positive relationships with your current/previous employer before you leave for a new role, as hard as it might be, as your future employer may ask for a background check or a reference.
Before leaving employment, consider how you might adjust to being unemployed. It might feel like a relief initially to be out of a difficult or stressful job, but you will also lose your daily structure, motivation and sense of purpose. Unless you can handle waking up in the morning with a "What am I going to do today?" feeling and won't worry about your decreasing bank balance, think twice before quitting your job.