For temporary renewals, there is very little benefit in depositing your documents at a local DGM sub-station. The only step you'll save at DGM in SD is going to the payment window, otherwise, the wait time will be the same. The local station does submit your documents for you, so you do also save the time of uploading them online at home - for whatever that may be worth(?).
For those renewing permanents, you can do the medical at a local DGM and save an extra trip to SD.