It will depend on coat type and I think there is a lot of variation from cocker like to poodle like and everything in between.
I had Flo groomed and clipped last summer and regretted it - she came home looking like this... (More like a poodle than a cockapoo)
She hasn't been cut since and now looks like this with lovely long, soft, scraggy fur I can sink my fingers into.....
Her fur is around 3 inches long but is quite loosely crimped, not that curly, so doesn't seem to mat that much. I brush her about once a week and sometimes have to spend a little time in the evening brushing out the odd matted bit while she is having a hug. I don't like using scissors in case I nick her so I just gently work on matted bits with a small slicker brush and they come out.
I must say I've never noticed her coat change from puppy to adult, like others have mentioned on the forum and it didn't seem to start matting more as she got older. She is now 14 months.
I take Flo to the groomer about every two months to be thoroughly washed and brushed through and will just get a light clip next time no shorter than 2 inches.
Now if I had 4 dogs like Kendal I would probably think differently as I would probably be brushing dogs for at least 1 hour per day if kept too long!!!!!
Also each dog is different and some tolerate or even love brushing and grooming, others hate it. It would be impossible to keep a cockapoo's fur long if they hated being brushed.