Sometimes you have a layer stack that is rather involved, or even just some color modifications that make it difficult to know what layer to make a selection from for the next step. You most likely want a selection from something that represents the current state of the file. How can you do that?
Make a merged visible layer at the top of the stack using the four key shortcut <Ctrl><Alt><Shift>E – [<Cmd><Option><Shift>E] – and use the merged layer to make your selection. The problem is that you have added another pixel layer to the file.That added pixel layer has two downsides. First it increases the size of your file. Second, it renders adjustments below it inaccessible. The solution is really pretty simple. Throw it away.
Once you have used the layer to make your selection and added the needed adjustment layer above it the layer has served its purpose. Removing it has no effect on the file visually, it simply eliminates an unnecessary layer full of unwanted pixels.
My practice is to keep pixel layers at the bottom of the stack as much as possible. Retouching on blank layers and other pixel based corrections are also kept at the bottom. This means that color overlays, adjustment layers and such can be stacked on top and remain modifiable. If you are a fan of Smart Objects this may not be an issue for you, but if you work in stacked layers as I do you may need this technique on occasion. If I add a pixel layer in the midst of a stack and it just has to stay there I label it “must keep” or similar and group the layers below it into something that helps me remember what is happening at that level and why.