The quality and reliability of the work performed can be significantly affected by whether a plumber is licensed or not. A large reason for this is the hiring of a plumber who has had to go through not just a significant amount of training, but also who has had to pass some rather rigorous tests. Plumbing is not an easy field, despite what many might think, and it takes a long time and a lot of effort to really master anything close to the "whole job" and all its plumbing "parts." A foundation like this can't be beat when talking about upstream problem-solving in a way that saves the homeowner both time and money and doesn't sacrifice either in coming up with a solution that meets all code concerns and works. Also, there is the simple point that many licensed plumbers are just plain better and use better materials than unlicensed types, who are more likely to use "impermissible" changes that do save money "up front" - but at what cost? - both in plumbing jobs that are just not done in a way that will last, and in possible "liabilities" if something should happen to go wrong.
Another vital aspect to consider when hiring a plumber is the level of accountability and protection you get with a licensed professional. Licensed plumbers usually have insurance that covers them in case they injure themselves or damage your property while doing the job. If plumbing goes wrong, the potential liability is enormous, and you would surely rather have the coverage that comes with a truly insured worker than risk having an unlicensed, uninsured worker do the job. On top of that, even if plumbing doesn't go wrong, a subpar job can lead to just as many problems, if not more, down the line. Beyond the basic protections, hiring a licensed worker gives you a way to ensure the job gets done right the first time and a way to resolve any issues that pop up if it doesn't.
It may be tempting to go with the least expensive option when it comes to plumbing problems, but in the long run, going with a licensed plumber is usually more cost-effective. Licensure in plumbing requires the course of study to learn about the durability and quality of materials used in the trade. This education, coupled with hands-on experience, allows for the reliability of a good quality plumbing job. More often than not, a plumbing problem that you pay to have fixed also comes with a warranty. That means you’re paying for a job to be done right the first time or else you’re not paying for the job to be redone. And as we all know, redos cost extra. Go ahead and pay up for a good plumbing job the first time around.