The answer to this question depends on several things
Is it a small or a large pet? Or is it more than one pet? More animals are more likely to cause a nuisance.
Are you going to rent an apartment or a single-family home?
Example: a large dog in an upstairs apartment is not wise. Neither is letting a large dog do its needs in a garden!
Does the tenant take good care of the pet?
Example: a litter box needs to be cleaned regularly otherwise it causes odor nuisance.
Are the pets well trained?
Example: a dog stays at home alone and lets the neighborhood know all day long (by barking) that his owner is not at home.
These points determine for the most important part whether having a pet causes nuisance and whether it is wise to keep a pet in a rental home...
“Concretely: the tenant must ensure that having a pet does not cause a nuisance in and around the house.”
In the rental agreement there is a standard penalty clause if there is nuisance caused by pets. This is what this penalty clause looks like (may vary per project):
“In principle, therefore, pets are allowed.”