You honestly don't need them, and they can even end up lagging behind your Sim so your Sim just stand there waiting for it to unlag so it can do what you planned to do with your Sim. Noticed this can happen when running through some stairs.
Resources are just not needed for the spellcaster, you get a potion as soon as you discover them and with a nice shelf system you plop all potions on there and then just cast the copy paste spell directly on that potion on the shelf and you'll get a new potion to use immediately without having to clutter up the already hopelessly cluttered inventory any more. No need to brew at all. Granted you can avoid the spell and play more normal and then of course resources come in handy, but the spell is always there to tempt you, stay strong ;)
That spell is horrible for gameplay, in my opinion.