Having used IntelliJ, the biggest advantage of IDE for me is the speed with which the errors are surfaced allowing me to correct them way more quickly than I could ever do in vim. It is so much more easier to find where things went wrong and how. That lets me focus on the logic instead of wasting time on things like fixing misspellings. Also totally agree with the ease of refactoring - it basically gives you the time and confidence to iterate freely.