Is it useful to upgrade MacBook Pro to 16GB RAM? How does an additional 8GB of RAM impact performance for the latest 13-inch MacBook Pro? 

It is used for graphic-heavy apps — Sketch, Design, Photo and image editing and to power a LG 21" display.

Does the additional RAM help improve display performance or does more RAM mean apps will not run out of memory?
With the GPU - the extra RAM won't make any graphics faster in my opinion. Running "out" of memory isn't something that virtual memory allows - and when you start to get under memory pressure the apps can release memory to the system and the system starts to slow down as memory swaps. At some point, performance suffers - but I'm having a hard time justifying cases where 16 GB of RAM is the "straw that breaks the performance camel's back".

I'm in the process of evaluating this for our company. Traditionally we have predominantly maxed out memory in our MacBook Pro fleet, but I'm probably going to split our orders 50 / 50 to see if we really need 16 GB RAM for our pro users.

Even our photo department processing 50 to 100 megapixel images in Capture One or Lightroom - we're struggling to justify more than 8 GB of RAM.

Once we have about 10 of each model, we will re-measure the RAM needs. My suspicion is we're being overly cautious and could go 90% smaller RAM and 10% larger RAM.

The reasons for this are:


The apps we need just aren't RAM hungry with the better frameworks and memory management on macOS.
The penalty of swapping to the NVMe based SSD is no longer a deal breaker for people that only occasionally push their Macs into memory pressure makes this a slight slowdown as opposed to a crawl when swapping used to hit HDD storage.
Statistically - our fleet of Macs just doesn't enter memory pressure. 


Basically, when our developers and designers are waiting - it's for file transfer, for network and the machines aren't the bottleneck to productive work. Yes - I can benchmark situations where I can exhaust memory, but in practice - people in that situation know they have too many other chrome tabs open, or outlook has hung on them or there is a memory leak and they can log out and clear that issue for days to come.

Unless you 100% know you have to run multiple OS at the same time, are a heavy windows user (we have some that allocate 4 to 6 GB of RAM to a PC and still work fine with 8 GB of RAM! on the Mac) the chance that you need 16 GB of RAM is slim. I would advise most people to spend that extra $$ on AppleCare or on new software or on books and training to make you more efficient rather than being "safe" with the maxed out RAM.