Advantage of using a database snapshot for reporting purposes
Using a database snapshot located on your production OLTP server will, in all likelihood, make performance worse. There are two main reasons:


Extra write overhead. Snapshots are copy-on-write, so this will obviously impact performance.
A snapshot will share pages from the old database on disk, but it uses its own memory in the buffer pool. If you have a large table, it will end up consuming memory for both the OLTP database, and the snapshot, even for the unmodified pages. You can end up with a lot of additional memory usage because of this, which can lead to more disk I/O if your server doesn't have loads of free RAM.


So if you're trying to make reporting less intrusive on only a single server, you're probably better off just querying the OLTP database and using WITH (NOLOCK) hints, and then reigning things in with the resource governor if needed. Beyond that, look into some kind of scale-out system (log shipping, mirroring, etc.)