A bar fridge is typically smaller than the conventional refrigerator used in the kitchen. The purpose of a home bar fridge is to keep beverages and mixers at the ideal temperature for immediate serving. Usually, you can manually adjust the temperature in a bar fridge. You might choose the optimum temperature for the fridge based on what you're storing at any given time.
Bar Fridge Deficiencies
One problem with many small bar fridges purchased for the home is that they don't actually maintain the proper temperatures desired in a bar fridge. Part of the reason for this is the fact that every time the door is opened, a high percentage of the cold air in the unit is lost. When purchasing a bar fridge, make sure that you buy one that is adjustable to lower temperatures if you want to serve drinks that are properly chilled.
Because your fridge gives you the ability to set the temperature yourself, you should adjust to the temperature for whatever beverage you store the most of in the fridge. The majority of domestic beers are best when served quite cold. This type of beer should be colder than 40 degrees. Pale ales should be kept slightly warmer, but no warmer than around 42. If you prefer very flavorful beer like many varieties out of Belgium, you'll want them even warmer. Around 50 degrees is right for beer like this.
Wine has more complex temperature requirements than beer. While white wine generally needs to be kept cool, the difference between varieties can be quite extreme. Sweeter wines should be served colder. A sparkling wine or a very sweet white should be served between 35 and 45 degrees. Drier and high quality white wines should be served at around 55 degrees. Either keep your fridge set at the desired temperature for the drink which needs to be coldest and let others warm up slightly before serving, or only place the bottles in the fridge to be cooled a few hours before serving to avoid over-chilling them.
Having an actual refrigerator thermometer inside your bar fridge is a good idea if you're trying to hit specific temperature targets for your beverages. The dial setting and the resultant temperature is not always exactly the same, and some fridges only have dials with an intensity rating rather than temperature-specific controls. If your bar fridge is primarily being used for chilling wine or beer, you can get specialized units that allow you to keep different zones in the fridge at different temperatures.