I have been on this forum reading most for a while now and I want to ask a stupid question.....What is unlocking a phone do for ya, what will it allow you to do?
Don't worry about it, it's not stupid at all.
A locked bootloader prevents the user from flashing any system images (ROMs, SBFs, etc) other than those signed and protected by the manafacturer or carrier (Over the air updates).
When it's unlocked, we can mess around and flash files to the system's filesystem, making it easy to root, ROM and remove the bloatware.
That being said, rooting is not impossible with a locked bootloader. Unlocking just makes things very easy.
The reason why companies lock the bootloaders is to prevent the end users from doing dumb things to their phones, making troubleshooting and fixing the problem hard for anyone who doesn't know what they're doing. It's not that they are jerks, but they need to do it to make things run smoothly.
Of course, the solution (in my opinion) to all of this is to lock the bootloaders, but then let the user unlock them (a la HTC). This strains out those who know what they're doing, making things less of a hassle, pleasing the companies, troubleshooters, regular consumers, developers and the people who love to play around.