It really depends on the end user. If you could not find any use of the PSD design files you could just opt for the Standard version. You will only pay the difference if you want to upgrade later.
Please help our moderating team work more efficiently by not sending us support questions via PM. You can read more about how AppThemes support works here. However, you can send a PM to follow up and remind me if I missed your support request/thread.
I have also responded to your question in another thread:
Originally Posted by pepsi
The Photoshop files contain details of the theme layout such as colors, sizes (width of all the pages, header bars, sidebars, boxes, etc), for every type of page available, so when a web designer is looking to make changes to to the theme layout, all this information is readily available. Yes, they could potentially collect this information themselves, however it can be time consuming. It's ultimately your decision if you want to purchase the developer edition in order to have access to the Photoshop .psd files, but you can always upgrade from a standard to developer license at a later time if you need to anyway. Thanks.