When would you use a perspective view instead of an isometric drawing

And isometric only shows three flat views of your object where as, perspective looks more realistic. If you object is simple, use isometric. If it's a lot more detailed, I suggest using perspective. It's just a little more difficult to do

When you want to get a more realistic view. Everything we see is in a perspective view.
For example, look at a standard housebrick rotated at 45 degrees. The rear vertical corner will appear to be very slightly shorter tthan the front vertical corner.