There may be a valid rationale to use potassium citrate as a supplement for those who are interested in improving beta cell function (i.e. diabetes) and insulin sensitivity.
Although the sample size is small, the research method for “Effects of potassium citrate or potassium chloride in patients with combined glucose intolerance: A placebo-controlled pilot study”, seems to hold its own.
Conen K. et al., conducted this double-blind, placebo-controlled study with 7 males and 4 females ages 47-63 years old who were glucose intolerant (an umbrella term for metabolic conditions which result in higher than normal blood glucose. Pre-diabetes, type 2 diabetes, impaired fasting glucose and impaired glucose tolerance is defined by the World Health Organization as a fasting blood sugar level of 6.0 mmol/l) and found that both systolic and diastolic blood pressure, beta cell function and insulin sensitivity were significantly and positively affected when given 90 meqs of potassium citrate when compared with potassium chloride. They concluded that the citrate anion (The first intermediate of the citric acid or Krebs cycle, it plays an important role for fatty acids and it acts as a carrier for acetyl-CoA, and then synthesis for fatty acids.)  is responsible for the insulin-sensitizing and blood pressure lowering results.
Yet potassium itself may be more than a viable piece of the diabetes/insulin resistance treatment puzzle. One’s own genetic  mutations (KCNJ11 gene and KCNQ1 (specific to the Asian population) affect potassium channels that influence insulin secretion, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3197792/.
Potassium:

1. is a necessary nutrient in normal skeletal muscle and nerve function (and we know that skeletal muscle insulin resistance is the primary defect in type 2 diabetes)
2. works with sodium to maintain fluid and electrical balance for the cell membrane.
3. is required for optimal heart, adrenal and kidney function.

Low potassium levels can result from fluid loss (from perspiration, vomiting, or diarrhea); excessive consumption of caffeine, salt, or sugar which many folks do on a daily basis, as well as, certain medications and natural supplements deplete potassium stores (aspirin, ACE inhibitors (captopril, enalapril), choline magnesium trisalicylate, colchicine, corticosteroids, thiazide diuretics, laxatives, sodium bicarbonate,  Glycyrrhiza glabra and ramipril.
Potassium researchers recommend a diet that maintains an optimal sodium-to-potassium ratio of 1:5 or less, http://www.anaturalhealingcenter.com/documents/Thorne/monos/Potassium%20mono.pdf.
Potassium recommendations for adolescents and adults is 4,700 mg/day, for children: 1 to 3 years of age is 3,000 mg/day, 4 to 8 years of age is 3,800 mg/day and 9 to 13 years of age is 4,500 mg/day.
Foods that are good sources of potassium include: salmon, tuna, turkey, clams, avocado, white mushrooms, spinach, kale Swiss chard, collards, broccoli, blackberries, cantaloupe, grapefruit, artichokes and tomato.
If you are not able to meet potassium recommendations, using a supplement seems prudent.  There are certain population groups like the elderly, pregnant women or children, those with kidney issues, ulcers or anyone prone to metabolic alkalosis that should not use potassium supplements. Any nutrient supplementation should be supervised by a doctor.
If potassium citrate can work as an insulin sensitizer while preserving beta cell function, it, along with other natural supplements like magnesium and chromium should be considered a first line option in diabetes treatment before using pharmaceutical drugs that have long lasting and more severe consequences.