A finger guard / bolster is meant to help prevent your hand from accidentally sliding forward onto the blade. I find them useful with fillet or boning knives b/c my hands are going to be slimy. At the same time, I don't want their addition sharpening headache, or need their slippage protection with other knives, so the rest of my knives are unbolstered.
IMO, the big, thick, full length bolster found on many modern German knives provide little pros and a lot of sharpening issues. The smaller bolster of vintage German knives, and 3/4 length bolster of better models do the same thing without the sharpening issues.