Does it send conflicting signals to your body to do weight lifting and cardio or HIIT in the same session?
If you look at your training in terms of long term success and long term health, you should incorporate different forms of exercise. Have a strength training component, a cardiovascular component, and a mobility/flexibility training component. If you want to maximize one specific area of adaptation like strength or endurance or flexibility, then yes it does make sense to focus most of your effort and time training specifically for that. But for most people a blend is best for your health.
At the Brentwood YMCA, we do strength, cardio, flexibility every Boot Camp session. All three of these things will give you better health and longevity than just focusing on one of the components. Evaluate yourself in case you are emphasizing one type of training over another. You probably need to work more on what you automatically shy away from.