Helping avoid bad investments is actually an interesting one. Significant value is added by preventing a catastrophic loss.
Yes, additional savings can be made by understanding the opportunity cost. Tax savings can be made by strategic planning. Proper asset allocation can balance the best expected return with a minimum level of risk. But sometimes there is a huge additional risk of an underlying investment without the appropriate level of potential gain and without the client realising it (double whammy).
If the advice is coming from Uncle Arthur, hot tips from a cabby, special software or a cold call, always remember that in the optimum 'efficient' portfolio (which is as good as it gets) RISK = RETURN.
Unfortunately, without sound advice, it is really easy to add risk without the appropriate return.
The chance of losing all or a large portion of your investment is simply not worth it. You always need to consider the potential downside - and what can (and sometimes does) go wrong.