What are the pros and cons of the FeLV/FIV vaccine?

I rescued a little abandoned kitten last week who was extremely malnourished and covered in fleas. It took some work and the istance of a vet, but I got her back to health. I'm supposed to go back next week for her shots, and was wondering what the pros/cons of the FeLV/FIV vaccine are. Would you ultimately recommend it or not? Please help as this is the first time I've ever owned a cat.