Variable assignment and simultaneous check of the return code in conditional statements

What are the contras for writing bash scripts like in the example below? Would you separate a variable assignment or a function call from the check of its return code? If so, why? What is wrong - if anything - with this kind of conditionals?

local return_code=0
if username=$(get_username "${user}") \  
   && is_from_earth "${user}"; then  
   echo "${username} is an earthling"
else  
   echo "ERROR: no name or not from the Earth"  
   return_code=1 
fi