It saves money especially if you have alot of high draining devices like small digital cameras, wireless mouse, lot of remotes, radio control transmitter, MP3 player, CD player, Flashlighs, and the list goes on..Overall any rechargable nicad or NiMh will save itself and more over its lifetime.
where 2 decent sanyo NiCads cost me 5.99 (for 2 packs less for more qty) and last 5k+ charges, and 2 energizer or duracell AAs at 1.99 (at a convenience store) take that times 5k charges !!!!!!!!!!!!!!!!!!!! and all you would have spent was about 75 dollars to set yourself up with a good flow of charged batteries, Nicads have a better hold over time charge, and life expectancy.
Although I use NiMh cells only in devices I use constantly, and keep only about 6 extra with 4 in charger, I have 24 AAs, 4 AAAs, 4 D's in NiMh, in Nicad I have 64 AA's, 12 AAA's, 18 C's, 8 D's. All sanyo. I also have several unassembled sub-c cells and some sub-d cells laying around, both are very high mah ratings.
To get you started finding nicads cheap I will point you here although I rarly goto them anymore for batteries.
www.Towerhobbies.com