If you like swinging streamers or nymphing while wading, a 4-5 wt switch is great. Be prepared for a learning curve on casting...and don't buy a switch just to lob out crappy roll casts. So much more effective if you cast somewhat properly.
The only cons in have found are: sucks if you find fish rising all around you and your stuck with a fat scandi line. And they aren't great in really low flows if nymphing, as your mends can easily rip your indicator out of the water. For medium to high flows a switch is great, and you can easily cast an indicator rig 60 ft which is nice during runoff. For swinging it's always good, but can be a pain to strip at short distance (you will have to toss line back out to cast again)