Yes, fans are important for a few reasons - not just to develop thick stems. They are also necessary because stagnant air will cause a humid microclimate around the plant which will cause the plant to slow photosynthesis, slowing growth. It also reduces transpiration which will cause calcium deficiency in the leaves leading to tip burn. The humid microclimate also leaves the plant more susceptible to molds/mildew as well as other diseases.
ETA: if you only have 1 plant, you don't really need a fan on it, but if you have a bunch of plants grouped closely together, you definitely should have some ventilation...
