A callable bond:

would usually have a lower yield than a similar non-callable bond.

is attractive to the buyer because the immediate receipt of principal and premium usually produces a higher return.

is more apt to be called when interest rates are high because the interest savings will be greater.

generally has a higher credit rating than a similar non-callable bond.

is attractive to the issuer because it allows the issuer to prepay outstanding debt if new debt can be issued at lower rates.