I am going to upgrade to a 120 gb SSD and install my OS on it. I currently have a 1 TB WD HDD and will use it to store excess stuff. But some people have been telling me to completely format my old HDD after I am done installing windows on my SSD. Why is that? Also, My HDD has 3 partitions and I do want to format my current C drive on the HDD but I dont see the necessity to format the entire HDD. Please tell me what should I do since I only need to format my current C drive. Also, will booting up with my SSD and HDD(with it having my old windows files) affect it before I format my current C drive?