Internal wall insulation (IWI) can be worth it in certain situations, but it depends on a variety of factors such as the condition of the walls, the age of the building, and the type of heating system used.

Here are some potential benefits of internal wall insulation:

1. Improved energy efficiency: IWI can help to reduce heat loss through the walls, which can lead to lower energy bills and a more comfortable living environment.

2. Increased thermal comfort: By reducing heat loss through the walls, IWI can help to improve the thermal comfort of a building, making it easier to maintain a consistent temperature and reduce draughts.

3. Reduced noise pollution: IWI can also help to reduce noise pollution, particularly if the insulation includes acoustic properties.

4. Preservation of historic features: In some cases, IWI may be a good option if a building has historic features that cannot be altered on the exterior, but still require improved insulation.

However, there are also some potential drawbacks to consider when it comes to IWI, including:

1. Reduced living space: IWI takes up space within a room, which can reduce the usable living space within the property.

2. Risk of damp and mould: If IWI is not installed correctly or in the right circumstances, it can lead to issues with damp and mould, which can be damaging to the health of occupants and the property itself.

3. Cost: IWI can be expensive to install, particularly if the walls are in poor condition and require significant preparation work before insulation can be installed.

Overall, whether IWI is worth it or not depends on the individual circumstances of the property and the needs of the occupants. It’s important to speak to a professional insulation installer to determine the best insulation solution for your property.