Many windows have a trim between the frame and the wall on the inside and/or the outside. These serve to tidy up any irregularity of the plaster or brickwork etc.
These will be pretty much maintenance free, but sometimes can come loose or be disfigured by years of redecoration etc..
We can fit completely new trim, or replace existing trim which can make a significant improvement to the appearance. They can also keep draughts at bay, where movement over the years, has caused joints to crack.