Above: quick sketches from TV all made because the people had interesting hairstyles. Pentel Pocket brush pen in the in-studio journal which is a Fabriano Venezia, 9 x 12 inches. Verso page contains some sketches on coquille paper glued over other "failed" sketches. Click on the image to view an enlargement.
I believe strongly that you should not tear pages out of a visual journal—those actions are usually done in haste when you really haven't had a quiet moment to assess your latest, non-Turner non-masterpiece. Let it breathe, give it a moment.
I encourage people to keep such pages as well as not cover up "failed" drawings with collaged sheets of paper or other paintings, because I believe those sketches hold gems of insight and understanding in the development of our observational skills.
That said, I think you're all grown ups (according to my blog stats 99.9 percent of you are), and you need to do what works for you.
So while I would prefer that you institute a moritorium on covering up work that today offends you, if after awhile you find that it is best for you and your constant production if you do cover up something, well please do so.
To make good on my sincere encouragement I'm showing you a page from my in-studio journal where I did something very rare—I covered up a less than mediocre sketch on the verso page, with sketches on different paper which for other reasons I preferred to keep. Now the top sketches, done on coquille paper are not stunning either, but to me they capture a little something of the evening and allow me to fit the evening on one page spread and that was important to me. It just seemed right.
Just as it seemed right to paint over the two faces at the top of the recto page. (What I really like about this page spread is that man with the COOL hairdo. I have been fascinated by hair lately and that's actually what I started to write about until I realized that I had something totally different to say.) Sometimes a journal page is like that too. So go for it.
New journal keepers are most prone to make the mistake of tearing out or covering up "offending" pages. But even experience journal keepers might be quick to do this if they think they have to "present" a certain level of "quality" to the world. Forget that. Remember that the journal is first and foremost for you. I call it a "mistake" to tear out or cover up pages because I think that to a certain extent you have to retain these pages until you have a chance to learn something from them about your process that can be useful.
Just do me one favor—before you cover up a page of work, let a couple hours at least pass. Look at the page with fresh eyes to see if you can mine that page for information about your skill, your need to work on something, your day, your progress, your process, your lack of focus, your insane need to be private (that's simple don't show people your journal).
The same impulse that also leads people to tear or cut pages out of their journals might be leading you to cover a page. If you look, with a fresh eye, at your work, after taking a deep breath you might see that action isn't the one you need to take.
If however, after looking, you decide it makes more sense to cover the page with collage or paint, than do so. Just make more pages.