Bad things about daddy long legs?

The term daddy longlegs is ambiguous. In Canada, the United Kingdom and Ireland it refers to craneflies which are harmless insects. In the United States and Canada it can also refer to a harmless arachnid harvestman (Opiliones, not a spider) and in Australia it usually refers to the cellar spider (Pholcidae). The latter does have a venomous bite but its effect on humans is minor.

The harvestman does not have any venom at all, let alone harmful toxins.