The better the color correction of the objective, the better the scope will perform with various color filters and polarizers. This will allow you to see and photograph detail, even things like photospheric faculae in the center of the disk. The smallest objectives around, even a 50mm, can produce useful images. For instance, the sunspot data used internationally is based on the equivalent of a visual count with an 80mm long-focus refractor. The upper limit of usefulness in practice tends to have been around 6 to 8 inches with a refractor, larger with mirror telescopes.
Most users get there with a Barlow lens.