Formal:
* Are not consistently employed.
* Do not find consistent application.
* Are not routinely utilized.
* Are not invariably implemented.
* Have limited applicability.
Informal:
* Don't always come in handy.
* Aren't always necessary.
* Aren't a go-to option.
* Don't get used all the time.
More specific:
* Are only used in certain situations.
* Are not appropriate for every case.
* Have limited use in this context.
The best choice will depend on the specific situation and the desired tone.