Depends on the type of policy, you can have only 1 Access policy on a gateway. However, you can also have a Application control policy and a Threat prevention policy. Those policies combined form a Policy package which is installed on a gateway.
The only way to apply more policies to a single box is to enable VSX and then per Virtual System you can install a policy package.
On a CMA / SMS you can have many different policies, here the limitations will be more in the area of the number of gateways managed by the CMA / SMS. Policy packagescan be saved (copied) and be left alone without insatlling them on any gateway. In the early days (pre R7x? before db revisions) this way used as a fallback on policy changes.
Regards, Maarten