Yes, but.
a) Corporate trustee, family of four, the kids and parents are members of the SMSF and also (as required by law) directors of the trustee company. You die and want your super to go to your wife (but have no BDN), as there are three directors remaining the two kids can agree to split your assets between the two of them and cut your wife out. Nothing illegal about that, wife ends up with nothing.
b) Wife doesn't want kids to what you had intended to leave to them. She is the appointer of the SMSF, sacks the trustee and installs herself as trustee and then enriches herself. Again, no law broken.
Trusts are pretty complex legal arrangements. I'd always ask an expert but make sure you understand them yourself, don't rely on others.