Senior dogs have good manners and are housetrained. You avoid the puppy chewing and potty training stages.
Older dogs are mellower and require less exercise. They happily relax next to you rather than needing constant activity.
With senior dogs, you can see and prepare for any age-related health issues instead of being surprised later.
While still substantial, adopting an older dog means making a 5-10 year rather than 15+ year commitment.
Senior dogs are less likely to be adopted. Giving one a home brings joy in their golden years.
If you're retired and looking for a companion, a senior dog's lower energy level can be a great lifestyle fit.
As space runs out in shelters, senior dogs sadly face euthanasia more than younger pups. Adoption saves a life.