Why is it good to follow Photoshop Etiquette? It's the way of improving clarity of your work. If you want to be a high quality designer, it's very important for you. You will be work with colleagues and they maybe will hate messy PSD's files (like me :D). It's important to have some rules to achieve better workflow. Yeah, I can use Command (or Control in Windows) to choose layer what I want to, but I have still feeling that it's like a "work on junkyard". It's stinking, It's annoying and it's wasting time when you are looking for layers which you need merge into group, but the layers are far apart.
If you will working with messy PSD, this is the fastest way how work with it. Use move tool (v) and click on layer what you need with this setting in auto-select:
But Photoshop Etiquette is not only about layers and groups. It's about all workflow with designing something. It's about to have clean and clear workflow.
Keeping everything in one PSD reduces the confusion of which file to use.
Ironically, absolutes like “Newest” and “Latest” are bound to have edits later. It's best to just keep a general file name.
PSD inheritors shouldn't have to go hunting to find original assets. Proximity is key to avoiding wasted time.
It's better to have control over how the UI elements look than using browser defaults. You're most likely going to be asked to design them at some point anyways.
Having to be asked where you put a file is common, but it shouldn't be necessary if you learn to put it on a file share before even being asked.
The quintessential piece of etiquette: naming your layers instantly decreases confusion and improves acclimation to an otherwise unfamiliar document.
Happy layers have happy homes. Folders group like-items for easier navigation and editing.
Having too many layers hanging around usually results in an unnecessary bloat of file size and can affect performance.
If you use an element (logo, photo, etc.) in multiple layouts within the PSD, only having to edit it in one place makes a lot of sense.
Layer Comps & Smart Objects offer a way of showing multiple states or layouts without needing to build (and maintain) another PSD.