A blog is a silent, internal conversation; a cogitation, ergo, the blogger must be a cogitator.
For the rare artist who sells their work, what to paint is more or less a simple matter; more of the same with some leeway to deviate slightly and explore, dependent upon the strength, tolerance and complexity of the fan base. In a way the majority of artists are not so constrained since there is no one they need to please ... perhaps.
For most artists then the unsold works accumulate and gather dust, in which case the storage area might determine the size and substrate of the paintings. If the artist is producing art cards, aceo, of the 2.5 x 3.5 on paper format then the entire body of work could be stored in a shoe box. However if the artist executes pieces more on the scale of "Guernica" or perhaps, "La Danse" then the artist might require a storage space such as an old dirigible hangar.
If the artist produces small quickly painted works to maximize potential profit should something sell then storage and material costs would be kept to a minimum and thus allow the artist to continue to work and develop. The consequences of such an approach would be a size limit as well as an execution in a very specific speedy style and this seems to be a narrowly defined niche, though with obvious potential.
Size, substrate and storage are one issue while subject matter could be another though this is not a constrain for artists who produce abstract work in which case it would be an endeavor of pure design and technique with far more freedom. For representational artists subject matter is of concern. Some very skilled artists can paint ugly very well and with great appeal, but this is a rarity. Artists should feel free to paint those subjects they enjoy though they might also produce works they surmise have a broad appeal as well. The two are not mutually exclusive.