The residency is the path to specialization. There are a handful of veterinary specialties you can earn without a residency, but, for the vast majority, a 2-4 year residency is the only path to specialization. So, really, the question of doing a residency is: Should you be a specialist? Obviously this is a question you need to answer for yourself, but here are some considerations which may help.
Timing. There are many paths to being a specialist, but the most common is straight from vet school to residency (pathology, lab animal medicine specialties), or from internship to residency (for most others). Some people may be tempted to go into practice first, and then go to a residency. While possible (and even successful for some specialties- like radiology), read the post about taking time off before deciding on this path- it will be harder than a more traditional path.
Salary. Most, but not all, specialists make more, sometimes considerably more, than general practitioners. If you have chronic health issues or family obligations, you may be able to take care of them more easily as a specialist. Otherwise, the salary shouldn’t factor into your decision-making.
Academia. Although some universities are figuring out they should hire general practice vets to train general practice-bound students, the vast, vast majority of faculty are still specialists. If you want to go into academic veterinary medicine, becoming a specialist is really your best bet. And academia is pretty great!
Expertise. In a study we did interviewing senior veterinary students, those interested in specializing expressed the desire to be considered experts and sought after for their knowledge. As a general practitioner, you become more knowledgeable and proficient in a wide variety of domains. As a specialist, you become an expert in a single field. Both can be intellectually rewarding, but if you want the social status that comes with being The Expert, becoming a specialist is an easy path to that regard.
Time. Do you want to spend 2-4 more years of your life on your education? Or do you need to get on with things? This depends on your own life situation, probably largely determined by your family life. Along with this is the reduced income you will have as a resident relative to entering general practice. This is only relevant during the residency, though, as your salary will be much higher once you are done.
Flexibility. As a specialist, there will be fewer places in the country you can work. General practitioners are needed even in very small towns, but Americus, GA, does not need a board-certified veterinary surgeon. In general, as a specialist, you will work at a university or in a private practice in at least a small city.
Dedication. As a resident you will work long hours for little thanks and little pay. Can you suffer through that? Are you OK being treated as a minion for more time in your life? It is physically and psychologically tiring, so you have to be dedicated to the pursuit or you will be miserable.
There are a lot of great reasons to do a residency, but it is not without cost, and it is absolutely not for everyone. Talk to your friends, your family, and your mentors. It’s a difficult, but important, decision.