Especially if you have only been taking your photography seriously for a few months, you should be shooting in RAW.
1.) You're likely just finding your internal eye. A year from now, you will look back and find that the photo you thought was garbage is actually pretty remarkable, your RAW file will let you print it full size and correct it far better than a JPG will.
2. RAW is the raw data from your camera. Shooting in RAW will force you to be a better photographer, because all the easy-fix bells and whistles like Auto Lighting Optimizer don't work with RAW. Shooting in RAW shows you what mistakes you're making and doesn't let you get away with mistakes.
Learning to shoot, in my opinion, is only one part of the greater ecosystem of photography workflow. Learning how to edit your files and what to do with the images is the larger challenge. By shooting in RAW (or converting to DNG) you will be able to come back to these files in 5 or 10 years when you've accumulated a huge amount of knowledge and tweak them to your particular style, fixing exposure, contrast, and noise at a far greater level then you will with JPGs.
The "pro" photographers aren't just shooting photos and handing them off. They're manipulating their work, creating projects, and creating value far beyond just a simple photographic capture. When I shoot, I charge clients a matching hour for post processing for every hour of shooting. That's how important post processing is to me, and that's why I always shoot in RAW.
If file size is a problem, yes, you're going to have to boot for a new hard drive. You can get a terabyte for $100 these days. Another option is to get critical about your work and trash anything that isn't top notch. In my first year of shooting professionally I produced 12,000 photographs and in the end I kept 6,000 for my personal portfolio and passed maybe 1,000 on to clients. The rest were trash.
