I didn't when I started out. But I do now.
I do speech bubble placement before I do the art. So at first it made sense not to draw behind them, until it didn't.
It mostly started when my work started getting translated it would sometimes require word bubble to be moved or made smaller.
Honestly, going back and touching up old pages to clean up for translation was just way more work and much more frustrating than actually drawing the whole picture and then having it go under a bubble.
Now though I don't have translators for my work, but I've still made a habit of doing this, as it also comes in handy when I'm reformatting for long form (you have a lot more space for that, so when reformatting I can usually move the bubble out of the way of the drawings because I have the space, unlike a condensed page for print. It's also useful for if I I have the opportunity to reuse a background. I can grab it from a previous panel and not worry about pieces of it being missing.
Another plus is that you can use you panels for promotional art easily by just hiding the text layers. I don't have time to draw extra images to promote my comic, but sometimes a comic panel will turn out so nice that I can use that to help with promotional images.