I disagree, I find the create the component once work flow cumbersome and unwieldy, so there you are deciding what component you will use, and then you also have to finalise power rating, package etc?
so you guess you need a 1/4 Watt resistor, sketch up the schematic, do the sums and then decide a 5W fits the bill?
I would imagine that most experienced engineers know the power requirements for resistors by the time they start capturing the schematic. I'll do a sketch in the notebook and work all of that out, before I even open the CAD package.
Same thing with op-amps. Same thing with voltage regulators. You pretty much know what you're going to use before you start the schematic-drawing program.
or you have to decide on one package, then get to thinking about PCB layout and decide another package would work better?
Well, that happens. Say there's a mechanical constraint that requires a different-size connector, or maybe the purchasing people tell you that you can get a part in package A a lot easier than package B.
But here's the thing: LM317 in a TO-220 has a different manufacturer part number from LM317 in SOT-223. So, thinking about how you'd change from the TO-220 to the SOT-223, isn't it easier to have both LM317T and LM317EMP in your library? Each component in the library knows the correct footprint AND has a part number that the purchasing people can use to buy the correct parts. Changing from one to the other, at the design level, is a simple matter of deleting the LM317T from the schematic and replacing it with LM317EMP.
Then you regenerate the netlist (in Altium, you recompile the design and then update the board, in Kicad, like the old Accel, you generate a new netlist and import it into the PCB). You then generate the BOM from the schematic. No hand-fiddling is necessary, and stupid mistakes are eliminated (parts in the library are vetted, right?).
i find I get more errors and end up stuffing about way more, If I have to decide on component and footprint at the schematic stage, so I do have to strongly disagree
How can you get "more errors" if you place components on a schematic, instead of symbols which have no part number or footprint information?
I honestly don't understand.