A jack of all trades, a master of none.
When a photographer tries to be a jack of all trades, they may actually harm their business.
The Dilution Model [link to PDF] suggests that when a business tries to do too much, customers will have a lower opinion of that business. Or to reverse that, when a business specializes, that business will be considered to be an expert.
Which is the better inkjet printer: a machine that’s only a printer or one that’s a printer, a scanner, a copier and a fax machine?
Which has the best pastry: a bakery that sells only pastry or a store that sells coffee, soup, sandwiches and pastry?
Which is more knowledgeable about bicycles: a department store, a sporting goods store or a bicycle shop?
As a photographer, you have to do multiple types of photography to stay in business. But if you spread yourself too wide or if you’re just vague about what you do, you will reduce the perceived value of your photography.
A customer’s perception of your business directly affects how much they’re willing to pay for your services.