Result is an outcome produced . "As a result (of something)" introduces the result.
"Therefore" presents a more or less logical deduction. It means "my reasoning leads me to believe that…," or "that's why."
It's been snowing all day today and roads are slippery and treacherous. Therefore (not "as a result") give yourself plenty of time to get to your destination if you are hitting the road tonight.
It's been snowing all day today and the roads south and north of the capital are slippery and treacherous. A series of fender benders slowed the traffic to a halt on interstate 93. As a result (not "therefore") the state police announced a temporary state-wide speed limit of 40 mph on all public roads until further notice.