Why refinish a vanity
Many vanities were built at the same time and in the same finish as the kitchen cabinets. When you update the kitchen, matching the vanities keeps the house consistent. When you update just a bathroom, a new vanity color can change the whole room.
Moisture is the main challenge
Bathrooms see splashes and steam, so the finish has to be well bonded and fully cured before heavy use. Water damage around the sink base is common; swollen or delaminated wood should be repaired or replaced before refinishing.
Pair it with your kitchen
Adding vanities to a kitchen project is usually more efficient than doing them separately. Mention every vanity you'd like done when you ask for your quote.