The way I see it, if your character doesn't take up at least 70% of the intended panel, then you should probably have something to help contrast it with and even then, many people will still do minor shadings, tones or textures. I find very few in this day and age go for a blank canvas except again when the character takes up a great majority of the panel or the blankness is intended for setting some kind of mood.
Honestly, drawing backgrounds in all your panels, minus maybe a select few isn't going to clutter things, it's going to enhance it. There are plenty of works that put a great amount of background, be it scenery, tones or textures. Karin Suzuragi the artist for a couple of the Higurashi mangas had this style. Not once is their a blank canvas on page. Every panel has at least something to contrast with the characters. Sometimes it's a full blown scenery, sometimes its specific tones or textures and it looks beautiful.
But that's obviously a lot of time and effort so its no surprise many artists have to, tone it down a bit, pun unintentional. However, some of them go too far and a great example of this is Tite Kubo's manga, Bleach. Kubo has this irritating tendency to draw almost no backgrounds, shades or tones. He proclaims this is because he wants people to focus on the characters but many agree it just devolves them because there's nothing for them to stand out against and enhance them.
It gets so bad sometimes that he will draw two page spreads where his character takes up maybe 40-50% of the page and the rest is just this blank whiteness. It really comes off as lazy sometimes.