I think using wider panels gives your deck a bigger look as you don't see as many gaps.
Using the wider panels also means that you won't be using as many screws when attaching your deck panels to your decking frame. The number-one benefit I think is that you won't be using as many panels on your deck when using the bigger size. Panel gap also plays a big part in your deck-panel layout strategy. - EricL
In some respects it's a personal preference for how it looks. Personally, I prefer the look of wider boards.
At first glance wider boards will seem more expensive but, as Eric pointed out, you end up using fewer boards and screws and they are faster to install as there are fewer boards. - Adam_W
I went with the 90mm boards for both decks that I have done. Although I liked the look of 140 mm boards, I felt both my decks were not big enough to pull it off!
I have read wider boards have comparatively higher chance of cupping which needs to be taken into consideration while planning and installing. - Neo19
If you are doing an ultra-low deck the 90mm will give better airflow and wider gaps will help as well, my decking jig does 6mm or 8mm gaps and I personally prefer 6mm for being less likely to have something drop through the gap.
Cupping will look worse on a wider board and I wouldn't use a cupped board in a new build – at best you will put strain on the fixings trying to flatten it out. A well-maintained deck with proper fixings spaced at recommended intervals should resist cupping. - Brad