Google trends is/can be a part of your general keyword research.

Obviously you don't want to target a keyword that's on a downward trend.

Also, google trends give you no real idea as to search volume/competition, so it should be regarded as a potential factor in your keyword research.

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Google Trends is a tool that can be used to trace how the popularity of a particular word changes over time or fluctuates depending on a season. So it basically helps to predict seasonal traffic changes, which allows you to tailor your SEO/marketing strategy accordingly.

As you see, Google Trends handles just a tiny aspect of keyword research.

Google has a number of other helpful tools that can assist in keyword research:
- Google Adwords Keyword Tool
- Google Suggest
- Related Searches
- Google Sets
- Google Insight for Search
- Google Analytics

SEO software that has keyword research as a feature usually includes all the methods offered by search engines + third-party ones. Moreover, SEO software lets you summarize results suggested by various methods and analyze them, thus providing the best keyword suggestions.

Google trends will tell you things that are popular already thus informing you of fields that are already competitive and possibly saturated. By trying to find keywords from market samurai and etc, you are only limited by your creativity and out of box thinking, which leaves a (very slim) chance for you to stumble upon an untapped niche or one that isnt ridiculously competitive like car insurance :p

SEO software (if it is a good one, I'm not referring to any) usually helps organize data provided for free by google. If the software has good reporting features, it helps easily build reports for clients. In all, seo software should save your time in keyword research.

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Just like other warriors said, if you can use them together, it would be much better. Market Samurai tell you paticular keyword's exact searches, Googl Trends offers you the volume data of that keyword in months even years.