Winter grooming is more important than any other time of the year. Dogs adjust to the temprature very well and lets face it most the time they are indoors snuggled up in front of the fire.
Matted dogs dont dry properly, the mats can cause infection and bacteria when wet and they will actually make your dog colder with them than without them.
Rain, snow, mud gets stuck all over the place and dunking your dog in the bath and not drying and brushing out thouroghly can cause knots and mats so a full prroffessional groom out will help combat this.
Opt for a bath & brush only or ask for a longer trim - I actually find most people want a short trim in winter to help keep their dog drier and cleaner - if your really worried buy a jumper or coat for your fur baby.