I had rececently purchased a 3TB harddrive due to the value for money that it presented. The added extra 1TB and the lack of available sata ports on my motherboard fealt like a no-brainer. However, soon after installing the harddrive I slowly found that there were a number of hurdles that I had to cross.
First was my OS, after reading a number of posts online I found out that you really need a 64bit OS to support it. If you have one of the legacy OS such Win XP you can kiss that extra 1TB goodbye, it simply is not supported. But then again why are you still on Win XP ?
For me, this wasn't really a major problem. I was happy to quickly wipe my installation (because of the way that I had installed my OS - within a separate partition. Also, because I was using Linux, all I had to do was download and install the 64bit OS. However, I thought to myself what would someone with Windows do ? Some of the Windows install, especially the OEM versions, specfically only allow a 32bit install. This would mean that you either need to purchase an upgrade or a whole new version from MS - that extra 1TB is already starting to look not attractive.
Secondly, you need to make sure that you format it correctly. The legacy, I can all it legacy now, partition table format will need to be GPT. I had a whole lot of fun trying to figure this out - don't make the same mistakes as I did and check out my previous post.
Third, peripheral support. I have a number of harddrive enclosures and docks situated around the house. I use a harddrive dock next to my HTPC, the main purpose of this new HD was to use it with the HTPC. I found out the hard way that my dock did not support a 3TB harddrive since the dock had a firmware built in and it was 32bit. This has now led me to purchase a new dock.
Finally, this has not happened to me yet but it is theory - if you want to use the HD with another computer you need to make sure that it all meets the gotcha's mentioned in this post. This is something that you are going to have to remember and not take it for granted that it will just work.
There you go, the value of the extra 1TB looks like it is great value for money. However, you need to make sure that you are ready for it. I would suggest that you look at this post and review your decision carefully before you purchase that 3TB.