Instead of feeling sorry for myself when I lost my job in 2001, I started lifting weights to fill up my time. When I become employed again, I decided to keep it up.
In addition to increasing and maintaining lean body mass, there is improvement in bone density. This also tends to lower as we age. I am 43.
I started swimming in 2014 via TI: to learn and for relaxation. There was an overall stiffness I felt from lifting weights. I also felt that there was an element of endurance and stamina missing. I found running boring.
(The transition was rough for me. I was so programmed to "muscle my way" through the water. :-)) Swimming requires you to loosen up as you engage.
On the average, I have done 4 hrs of weights and 2 hours of swimming per week . ( I plan on doing more of the latter to further improve my stamina so I can get closer to my goal of a mile non-stop.)
Yes, you need both and I have experienced that swimming complements weight lifting very well. For instance, I could only do 10 reps max of pull-ups. After swimming for just roughly 2 months, I shot up to 18 - 20 reps. Indeed, swimming tasks your endurance muscles.
Stillness is the greatest revelation.
-- Lao Tzu
The light of the body is the eye.
-- J. Ch__st.