That depends, it would be annoying if you open lots of issues for minor, unimportant issues. But if you find a few major problems its good to report them. Of course its always ideal if you submit fixes as well, because there are never enough devs.

I think its better to detect something early even if there is not a fix as it at least can be triaged and others can fix it if the original reporter is unable to devote the time or whatever

Better ask the lead developers... :)