You would never get a permit to tag for frivolous reasons.
Depending on the animal and the tag, tagging is used to obtain different information. Habitat use and migration patterns are one of the main reasons. You cannot protect an animal unless you know how it uses it’s habitat (the place it lives).
For marine animals it can give amazing insight into dive patterns and hunting behaviour that would remain a complete mystery otherwise, they even have the capacity to give you information on the tilt of the animal in the water column! Tags can give detailed information on home range size and core habitat characteristic. Home range is the area in which the animal spends it’s time and core range is the area within the home range it utilises intensively. Capturing an animal to tag it also gives scientists the opportunity to take blood samples that they would never otherwise get which is very useful as, for example, you can find out more about the gene pool and how different populations are or are not interbreeding.
With the tags can also get information about the social structure of the different species.
When yo do the tagging is important to think about animal welfare, so you have to use the least invasive method possible to obtain the information needed.
The labels are particularly useful in species that are difficult to study.