I bought my laptop with 1 x 16GB and it is a bottleneck. On benchmark tests I was getting 30% lower scores than my USA counterparts who had 2 x 8GB.
2 sticks will provide you dual channel, so you will get better performance. Most games and modern app are programmed to work better with dual channel. Took me a while to work that out.
I think there is a thread bout it on here if you search threads by me. About my MSI laptop and the issues I had.