it an investment: you are directly building capability in your staff, and investing in helping the other person build her skills by paying attention to her career goals. This investment will build trust and contribute to retaining staff. The time it takes to complete a task will lessen as the person becomes familiar with the steps involved. In the meantime, if the work meets quality and time requirements, you're headed in the right direction.
A Word of Caution
Now that you're reducing your workload, make sure you aren't overloading your staff. Don't pile more work onto the already overloaded.
Use delegation to help you and help your staff grow. Look for interest and opportunity; define reasonable chunks based on skills and risk. Give people enough rope to move around, but not enough rope to hang themselves