Use fungicidal paint additive everywhere?

Products such as these are all good and well but they don't address the underlying issues as to why mould develops. Good airing of bathrooms and flow of air should be maintained as well as extraction fans and opening of windows to stop condensation and cold bridging. If the mould is treated and removed and good maintenance takes place then standard bathroom paints will suffice.

I would generally only use a fungicidal additive in areas where a moisture issue exists I.e in a bathroom that has ventilation issues that can't be solved easily as it can help to keep any bacteria at bay, but to answer the rest of your question using the additive will not effect the paint finish or colour as long as the paint is not thinned down to much with the additive, it doesn't make sense to use the additive anywhere else unless their is a treat of fungus or bacteria