I use Tor, but I don't use the Tor Browser Bundle... It's simple enough to configure my browser to use Tor without relying on yet another executable to do it for me.
The concept is that it's actually not as simple as it may seem. You're using the same cookie jar -- what if you inadvertently send back a cookie with the session ID of your public profile? You'll have flagged yourself as a Tor user and this can be tied back to your public IP. You're using the exact same browser fingerprint, which is more unique than you imagine -- it's not just a matter of useragent, but the combination of all information that can be obtained by a site about your browser. The EFF runs a demo site that shows this can be practically unique in many instances. You've probably enabled scripts on certain sites that may not need to execute JavaScript when you're viewing them through Tor. You probably have less restrictive rules around the injection of plugins that may expose your interface IP address, like Flash. You may do something shady and forget to cleanse it from your history (and/or enter private browsing mode). You may have an extension running that shares more information than you'd like, with either the site or the extension provider.
For all these reasons, TBB exists, and is the safest way (short of a live environment) to ensure you have a sanitized environment. At the very least, you should use a separate browser profile before you switch to an activity that mandates the usage of Tor, unless you're using it only for very rudimentary circumventions.
For all these reasons, TBB exists, and is the safest way (short of a live environment) to ensure you have a sanitized environment. At the very least, you should use a separate browser profile before you switch to an activity that mandates the usage of Tor, unless you're using it only for very rudimentary circumventions.