If you are going to do any serious CSS development and/or troubleshooting – you need to be able to see the site on as many browsers as possible. Generally – we have several browsers on several operating systems going at once so we can make sure our bases are covered.
Last week I built a mobile theme for a client and after a few refreshes on my iPhone – I decided I needed something easier and more developer friendly (I needed to view source). I use the “Develop” menu in Safari (Preference > Show Develop menu in menu bar) – and with that, I was able to choose my user agent (iPhone) – and then view how it would look using Safari which was much faster then using my iPhone – and I could easily view the source. If you need to do any development that depends on the user agent – don’t forget about this little trick!