From an engineering standpoint...
If you're designing piping for an industrial plant, this is critically important for laying out the pipe, choosing pipe size, sizing pumps and so on. Do it wrong and your plant will not meet capacity or you will spend to much money oversizing the system.
For a PC cooling system, oversizing the tubing and pump are more a point of pride than an excessive expenditure.
Nevertheless, were I designing a PC cooling system, I would try to use sweeping bends rather than small radius 90° elbows and would minimize fittings to whatever extent possible.