just curious as i want to see the reasons why people have both because the mac pro is my dream machine.
I have both. The early 2010 MP is the work horse desktop shared by my wife and I (it's pretty well set up with an SSD to boot OSX or Win7 and ~6TB of HDD space).
I have a MBP that I use when I'm at the race track to analyze data from the car. I also take it when I'm on vacation instead of my work laptop (a PC). The MBP also is OSX or Win7 as the track software is windows only.
I also have a Time Capsule and a Windows Home Server on the home network to ensure I have backups of everything on-line and a couple external eSATA/USB enclosures that I use for extra backups that are stored in my office at work or in the safe at home (in case of fire or theft). All our financial files and other sensitive information are on a disk protected using PGP whole disk encryption.
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I have a Mac Pro because the power speeds up my workflow.
Like Pressure said, it's not very portable and it's hard to move round. The MacBook Pro offers this.
If I need something I either connect to my network via VPN or carry an external HDD.
Anyways, I'm not sure what you mean by "music guy"; do you make music or just enjoy it? If the latter, you don't really a Mac Pro; an external HDD will do; personally I only have 3.2TB in internal disks, but I have 18TB in external drives to store my files, media, backups, etc..
just curious as i want to see the reasons why people have both because the mac pro is my dream machine.