Yes, I write everyday. Whether it is adding to an unfinished story, participating on forums like this one, editing or creating a lyric or making money on a content mill.....I write everyday.

I thoroughly enjoy writing.

No, I don't think it's necessary, however, writing is an exercise and so even if you are dealing with writer's block, you may find it rewarding to indeed try and write something every day. It could be a creative writing exercise if you are stuck on your manuscript. 

I don't have the time/energy to write everyday. Most of my writing gets done on my weekend. So, two days a week is really where I get all my writing done. I do try to read during the week as it doesn't take quite as much focus. I also like to read online stories for critique.

I think as long as you're building a habit of steady output, you don't have much to worry about. I haven't hit any issues with writers block by only doing two days. I've made a lot of progress, only its probably slower progress than others 

The 'writing muscle' is like every other muscle. The more you exercise it, the stronger and easier it becomes to use it.

The important thing is that it engages my brain and keeps me working (my fingers are typing, my brain is formulating a combination of words in a specific order, etc.? So e en if I’m not writing something for my current project, I can at least engage that creative part of my brain that makes me a writer.
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It’s like reviving your engine. You don’t expect to get anywhere, but it’s always useful to fire up the motor and practice going through the motions. Once, I had no phone and a ten minute break with nothing to do. I took out a pen and a napkin and started brainstorming names for my next heroes and villains.

As long as you keep writing, everything you do will help get you to the finish line.