Snehankur
I have Cubase AI 8 and Studio One 3 Artist. I haven't installed any of them, I thought they will put load on my DAW PC.
Only if you're running them at the same time, which isn't advisable anyway if you're using an ASIO interface.
My question is if I install them :
Will I be able to explore any good feature what my Platinum is not giving?
Yes and no. You can transfer files among programs, but it's not a seamless process. SONAR makes it very easy to export all your audio, which you can then bring into another program; and of course you can do the reverse. I don't think you can drag and drop between two different open programs but I haven't tried it...maybe it's possible. However cannot use Platinum features in Cubase or Studio One, or use Cubase or Studio One features in Platinum.
Will I be able to utilize Chord Track, Arranger Track, Note FX, MIDI effects etc and bring the results in Sonar?
Yes, but keep your eye on Friday's Tip of the Week, which tells how to do easy arranging in SONAR. The next one covers how to create a feature that's like Studio One's scratchpad, but is more flexible in some ways. Much of what other DAWs can do is possible in SONAR with a little creativity.
Will the VSTi installed by the process of installation of these two can also be accessed from SONAR?
Many of Sonar's plug-ins will work in other DAWs, but AFAIK the plug-ins in Cubase and Studio One are "keyed" to those programs and work only with their respective programs. At one point Cubase made MIDI FX based on the Cakewalk MFX standard and offered a "wrapper" to run Cakewalk's MIDI FX in Cubase, but those days are long gone.