“Are deep cleanings worth it?”

Only if you want to prevent bone loss, and eventually losing your teeth. The bacteria under your gums has been linked to systemic health problems. Problems like increased risk of Covid infection, Endocarditis, increased risk of heart disease, increased risk of Pancreatic cancer. So removing that bactrria is a healthy choice. Periodontal disease causes chronic inflammation which is not limited to the oral cavity, So is it worth it? If you value being in good health and wanting to avoid a loss of quality of your life than yes. On the other hand if you are cool with losing teeth, putting yourself at higher risk for chronic health problems and a declining quality of health/ life then, then no.