There is absolutely no downside to running synthetic other than the added cost. You can run it longer between changes, it doesn't break down with heat as quickly, it cause less sludge, and it has a higher resistance to gasoline contamination.
There are many myths about synthetic that seems to make people worry about it. When it first came out in the aircraft industry, there were some problems with. They had issues of it not mixing with mineral oils and a few other problems but those are all resolved and have been for decades.
Some people have complained about more oil consumption when using Mobil 1 5w30. I used to use it. My car seemed to use a lot when autocrossing on hot summer days. But that probably has more to do with the fact that it is 5w30 not that it is Mobil 1. I started using 5w30 Mobil in the winter and 10w30 Mobil 1 in the summer. It used a lot less. I now use Royal Purple in the same viscosities. It seems to use about the same amount.