Every time I change the bobbin. I use Qtips to grab all the fuzz. Then I add a drop of oil to the hook area. My big Bernina has a big bobbin. If I had a smaller machine I'd probably do the oil every other bobbin.

I have a front loading bobbin on both my Bernina and my longarm. On the Bernina I take off the plate and clean as you describe, and oil every 3 bobbins. My normal thread combo is Aurifil in the top and Bottom line in the bobbin.

The longarm I brush out the bobbin area and oil every bobbin change. I only remove the needle plate to brush out between projects. I have found I get 90% of the lint with the brush out and there are no feed dogs to be concerned with on the LA. I also usually quilt with poly top and bottom so don't get much lint. Definitely notice the difference when am working with a cotton thread, even really good cotton thread has more lint build up than poly which has very little. When I use a less expensive cotton like connecting threads or even YLI I get loads. Superior King Tut is not so bad.

I clean the bobbin area after each project or if I notice poor stitch quality.

I brush out the bobbin area after every change. But, I only take the plate off after the job is through. However, on my longarm, I thoroughly after every bobbin!

With my sewing machine, I take off the plate and remove lint after every second or third bobbin. There isn't anything I know how to disassemble beyond that. I'd like to get one of those little vacuum units eventually.

I peek at the area above the bobbin case with every bobbin fill (mine is a vertical bobbin), but only tear it down to clean and oil after every quilt. I change the needle then, too.

I try to clean after every project.

I'm trying to be more diligent by cleaning with my small brush every few bobbin changes and when I finish a project. Occasionally I take the hose of my vacuum cleaner and put it over the opening, with the bobbin out. I usually put a thin cloth over the end to see what I am pulling out. If it has been a while, I am always amazed at how much is up in there that I cannot get with a brush.

Every bobbin change if sewing with linty fabrics like flannel, and every other bobbin change otherwise. I totally dis-assemble the bobbin area. and I bought a vacuum attachment that I use to get into areas that the small brush just cannot reach. You would be AMAZED at the amount of lint that these suck out of your machine!

I clean out usually once a month or so and use those vacuum attachments made for cleaning computers, sewing machines, etc. I have a thin rubber hose that fits on one of those little attachments and I also use that to clean my dryer where the lint collects. I got my attachments at Menards and it cost about $12 dollars - well worth it.