thermal insulation keeps your electricity bills low, keeps the temperature more constant, and retains the temperature much longer if there is a power outage.
thermal insulation is really important for a chest-type freezer, not so much for a wine cooler. but then, cold air sinks down while hot air rises up, so the chest-type design does not make that much sense and you might as well have something that opens on the front.
and going a bit bigger will allow you to add water bottles, fresh water has really high thermal capacity, so some water bottles and a small internal fan help to keep the temperature even more stable.