Hey there
Not trying to make a provocative post, just need your personal opinion. My partner brought ProTools 10 to the studio. I can install it on the main  computer but I only have 50 Gb of disk space left. If it was any other DAW, I would want to install it for the VST plug ins, but PT does not read or offer VST. I am not seriously considering to switch, just want to know if it even worth of the consideration. It is 32 bits- we would have to upgrade it to PT 11 to make it 64 bit. I would also have to install all plugins I have in PT format. Which would adversely affect the disk space. But everybody using ProTools has such a great confidence that they indeed using professional software. Is there any advantage in using PT over Sonar PX3? Thank you.

Is there any advantage in using PT over Sonar PX3? 
 
Not if you have 50gigs left.
 
There's no need for it unless you have some firm requirements to work on Protools project files...

Well- it needs 20 Gb. The hard drive can be cloned- theoretically- I do not believe in it but in theory- it can be done- if it worth the trouble...

Not a cheap solution, but you could buy Vienna Ensemble Pro (a subhost) to run 64-bit VSTs in PT10.

Edit: re-reading it, I may have misunderstood the question. I use both Sonar X3 and PT11 (and previously PT10). From a hard drive footprint perspective, I would think that Sonar would be a better option, as long as you don't install all the extra sample content (same goes for PT). It's a perfectly capable replacement for PT, albeit with a somewhat different workflow.

Cloning a C drive is possible and I have done it successfully. I had a C drive that was making a very bad sound but still working normally. It was only 80 Gig as well. I have two drives C and D drive. D drive being used for data.
 
I bought and used Acronis True Image (after extensive research on the subject) and I removed my D drive and installed a brand new 500G drive there. I then performed the clone except I did it in real time. Not using the image. What happens in this mode is the computer reboots but does not go into  Windows. It stops before going into Windows and the program runs and performs the clone bit by bit.
 
Then I removed the old C drive and put the cloned C drive (D) into the C position and put the D drive back. Everything worked perfectly. Except I had to only reauthorise two things. One was my Wavestation VST and the other was Studio One. For some reason they were the only two things that new what had happened. I had to use an extra license for Studio One (you get 5) but they offered to give it back to me.
 
Everything else worked as normal and was none the wiser. You need to do something similar. You are running out of space and I was too and the thought of rebuilding my C drive was just too much. It would have taken a week. This only took an hour or so.
 
You have got nothing to loose by doing this because your C drive is still OK and could be put back in if it did not work for any reason.

If you do work for others a lot I would just install it for compatibility sake. "Yeah, I got ProTools"
 
EDIT:
Interestingly, my friend was asked the other day to engineer/record using Logic at a large venue concert hall here in Holland (Ahoy), where they ran a loop of 192 channels at 24 bit 96KHz (tv and radio and whatever could plugin using MADI at any point).
"Pro"Tools couldn't cope with it at all, just kept glitching and freezing, hence why they called him because their main engineer wasn't comfortable enough around Logic to risk running it himself.

As far as I can tell from experience, the only thing that PT 10 is better at than Sonar is reading OMF's and AAFs. Plus as the above Post suggests, its good for compatibility.

Pro tools is just another tool like sonar. I like pro tools I wish I was using it more often. I like steak, but I also like chips and mushy peas. Occasionally chicken is nice.... Occasionally I get food poisoning....

When I first started working in digital audio Pro Tools was KING! There are still times that someone off the street thinks that everything recorded in computers is called Pro Tools. You just had to have it to be legit.
Thankfully, those days are not completely gone but they are waning away. Word is getting around about these other tools out there. The first time I was trained on Cakewalk Pro Audio 9, I walked away saying to myself to watch out for that company. They really seemed to be on to something. Now I look at my own setups and I see Sonar 8.5 up to X3d. There have been some stumbling blocks here and there but I have always felt that Cake was on to the right thing.
Today, Pro Tools is not the necessity it used to be. I have not used Pro Tools in a long time and do not miss it.

I happened across this video a while ago where a user wrote into a guy and asked if he should switch from SONAR to PT. If you listen at 3:25 he makes a comment of having a friend in the Philippines who only uses SONAR and does "phenomenal work because he know the tool well." I think that is the ultimate point, especially when limited on time (as you say you are)... you can risk becoming "Jack of all trades, master of none." The comments to that video are also an interesting read.
 
Sidroe dropped a sage piece of advice to that effect a couple of months ago, which was basically "pick a DAW and learn it." They all are capable and have their own up/down sides. There is no substitute to dedicating the time to master the tools you have.
 
As a guitar player, I have seen (and stated) this numerous times... many new players buy an expensive guitar thinking they can "suddenly play" which is disheartening to see. The proficiency of the user counts orders of magnitude above any tool they are using.