I've had some of those long forms which can get annoying, however I think they're good practice to do anyway because other companies might also have long forms or similar forms, in which case the next time you do such a form you'll get faster at it as you can use the information from previous ones.
In my opinion interviews are worse as you don't have as much time to think - yet they can still ask you questions similar to what's on their application form or ask you to elaborate on something you wrote, whereas when you fill out the form you can spend as much time as you need. I'm notorious for talking ages to fill out the forms and thinking 'if they asked me that question in the interview, I'd be screwed'.
I also have some parts I don't know how to fill in/answer or the best way to approach those parts - recruiters want to see your judgment in those cases, whether you can avoid mistakes, and how well you express yourself in writing (for written response questions). If in doubt ask someone for advice or for them to check your form. (another thing you get the benefit of in a form as opposed to an interview)