side effect for increasing maxpermsize and max heap size

Can anybody explain the side effects for increasing the maxpermsize and max heap size?

I know that sometimes, we increase -Xmx when we run into the outofmemory issue. But I am just wondering if there is any side effect that I need to keep in mind when we increase the -Xmx. And how does increasing maxpermsize affect the runtime?

Thanks.