Many bands just pick a band name and then start making music. Bands spend hours designing posters, CD covers, T-shirts, and lots of other merchandise with the band name on it. After all that, it would be a huge bummer to have all that merch destroyed because another band has already trademarked the band name and owns all the rights to the name/logo. So before you invest heavily in the band, it's a good idea to trademark the band name.
If you're going to put days, weeks, months, and even years into your band's music, image, and reputation; be sure to take the time to ensure that you will own all the rights to the band name. Having peace of mind that the finer details of the legal side are all take care of will help you further your career. Plus, this will also ensure that no other band can claim the name and start mooching off of your success.