So what you're saying is that when you look at professional tracks, you see that they're hitting at 0 dB or close to it all the time. That's definitely true, but that's probably not how you should mix down your track. I say probably because it's really up to you - there are tons of different ways you can mix your track while you're making it.
Generally, you want to mix your track with extra headroom. Whatever the loudest elements of your track are will be mixed the loudest (duh), and you can decide what decibel level that is. I generally mix my kick and bass, the loudest elements in my tracks, at -10 to -12 dB. Then structure everything else around that, but quieter.
The reason you see the professional tracks hitting at 0 dB isn't due to mixdowns, it's due to mastering. Tracks that have headroom after mixing can be brought up to 0 dB using compressors, limiters, etc. Basically making the track loud+other tweaks to eq, compression, and other things. When you master, it's probably a good idea to do what you've been doing in listening to pro tracks, since that's a good reference to how you want your final track to sound.
Of course, there are exceptions - I remember reading GTA had everything in their song Saria's Turn Up clipping like crazy during the mixdown and they just slapped a limiter on it and called it a day. That sounds fine too. So I guess just experiment and see what works for you.