Depends, it's also good to know your limits. I can do plumbing but when I had my house re-piped damn right I hired a plumber. My house needs new asphalt shingles, I have done lots of roof work, but damn right i'm hiring a roofer. I know how to work on my truck and even have my friend's auto shop to do it in. I'm not doing an transmission rebuild there, I'll take it to a specialty shop. It will be done faster and I won't be a multi day burden on my friend.