I am a big believer in buying very good reels with good drags and multiple spools. For fresh water and occasional saltwater fishing a reel that handles 4-5-6 weight lines and a second reel that handles 7-8-9 weight lines will do a pretty good job for Trout, warm water, Steelhead, Salmon, Stripers and flats saltwater. If you are someone who has to have a 3wt and below rods then a light weight reel for these rods would be needed. You can stretch the use of the 4-5-6/7-8-9 reels by using Gel Spun backing. With these two reel sizes you can fish a wide range of rods and lines using additional spools.
This doesn't work with a guide as he needs a reel on every rod. A die-hard Salt water fisher will want to have more than one rod set up and ready to go. For the rest of us these two reel sizes will work quite well for a large range of fishing.