This summary is not the rule. The rule text controls.
A judge can keep out evidence even if it's relevant to the case, if it causes more harm than good. This happens when the evidence might unfairly sway the jury's emotions, confuse the issues being decided, or mislead people about what really matters in the case.
The judge also has the power to block evidence that would waste time in court. This includes evidence that takes too long to present without adding much value, or evidence that just repeats points that have already been made clearly.
The key word here is "substantially." The evidence isn't thrown out just because it might cause some prejudice or take some extra time. The downsides have to clearly outweigh how useful the evidence actually is to the case. This gives judges room to make judgment calls about what helps the jury reach a fair decision versus what gets in the way of that.
