Pretty straight forward question, I presume. Just as it says on the tin.
Well in theory, there’s no difference, but in practice, there is.
Right, sorry, I’ll show myself the door.
Practical skill is your effective skill value.
Theoretical skill higher than particular simply represents some “extra” knowledge that will speed up (practical) skill training.
Also IIRC theoretical skill is what determines when you learn recipies
Theoretical skill is knowing how to do something, while practical skill is actually being able to do it.
Usually you first get the theoretical knowledge and then practice (either with practice recipes or through on-the-job-training) to be able to apply it consistently.
A practical skill that’s too low will result in crafting taking longer and having an increased risk of suffering failures (which may just be lost time, but can also result in loss of materials, some of which may be hard to come by: it’s not great to lose the only SWAT vest you’ve found, in particular since a started crafting project no longer accepts any alternatives to the ingredients that were selected when it started [happened to me, resulting in two weeks of lost work and a crafting that couldn’t be completed]).