Twentieth-century deodorizers focusing on pet issues generally had a strong fragrance. Chemical solutions and odor removal processes at that time were often average at best. This necessitated strong fragrances to be added that would overwhelm unwelcome odors for several weeks. In essence, the fragrance moved into the house. Many times the fragrance was only a little less obnoxious than the odor it was replacing.
Twenty-first century innovations improved the odor removal process enabling the chemical solutions to have a light fragrance if any at all. The primary chemical development was a powerful pairing agent generically described as an odor encapsulant. Upon contact, it immediately neutralizes volatile organic malodors without leaving another odor. It is temporary unless the contaminants creating the odor are removed as well during the Cleaning process. Special synthetic fragrances, if desired, are designed to go with the odor encapsulant as it will neutralize organic elements in a fragrance.
Properly formulated odor encapsulants will also contain surfactants and soil-resistant polymers. The surfactants enable penetration into the fiber and substrate. The odor encapsulant can only work if it comes in contact with the odor. Odor encapsulants have sticky residues. So soil-resistant polymers need to be added to dry the residues limiting their soil attraction properties. Over time, odor encapsulants have been formulated in small proportions to add odor removal properties to many different types of urine products. This includes bacteria/enzyme, urine neutralizer, sub-floor odor sealer, liquid, and powdered oxidizers.
The primary mechanical development is a Water Claw that is designed to flush out 80 to 90% of any water, cleaning solutions, and/or contaminants in the carpet. This part of the process does much to remove the source of the odors even at the pad level. A bacteria solution, injected in the pad, is recommended to deal with any remaining contaminants causing the odor. This removal allows the odor encapsulant to effectively deodorize the carpet. There can be no odor or there can be no odor with a light fragrance. It can be argued that the job is better with no fragrance or with a light fragrance. Typically, products with a light fragrance dominate the marketplace.
One thing about fragrance, it is not about you, it is about pleasing your customer (mostly female) who have you in their house a few times a year. Whenever we have a new fragrance we take it around and make sure our female employees like it. Most nose dead cleaners (I am included with this group and do not make fragrance decisions) generally like fragrances they can smell, which usually means the fragrance is too strong for their female customers. Some cleaners leave too strong of a fragrance like they plan to move in with their customer. A good fragrance pleases for an evening and leaves the next day. You want to make a good impression with a pleasant fragrance so that they can be a repeat customer.