has more than 80 views, bad for performance:
User interface performance is directly related to (among other things) the complexity of the View hierarchy being displayed. This warning message is simply letting you know that you have a lot of Views defined in this layout and that it could lead to UI performance problems. The solution is to look at your layout and considering how you can simplify the View hierarchy to achieve the desired results with fewer Views. Or, alternatively, you can take this warning with a grain of salt and just test to verify whether performance is acceptable for your layout on the device(s) that you plan to support.
Nested weights are bad for performance because:
Layout weights require a widget to be measured twice. When a LinearLayout with non-zero weights is nested inside another LinearLayout with non-zero weights, then the number of measurements increase exponentially.
It's always better to use RelativeLayouts and adjust your view according to the places of other views without using specific dpi values.