The use of degrees with a heading in LTCC has come about as best practice. This is because some pilots in the past have confused a heading instruction with a level instruction.
e.g. descend fl220 fly heading 250 reply - descend fl220 heading 220. We also try to give headings that end in 5's if possible.
Some controllers also don't use the phrase fly heading because some foriegn pilots have confused fly heading with flight level!