KMP probably won't be generating positive income, although other MLPs (mostly non pipelines) do. E&P MLPs, for example, typically produce positive income in box 1 of the K-1. But you will need the passive losses when you sell in order to offset some of the gains from your reduced cost basis. So if you do not track the passive losses you will pay more tax than necessary when it comes time to sell your position.
And there's another factor which I am less sure of the details. When your cost basis reaches zero you pay tax (LTCG) on your distributions in the year you received them. However cost basis reaching zero is not as straightforward as it sounds. Non-recourse losses may delay reaching cost basis of zero and I think (but not sure) that if you have passive losses, you can also use those in determining whether you have a cost basis of zero and thus delay paying tax on your distributions. Reason I'm more vague on this is that I'm not down to zero basis on most of my MLPs yet and will check this when the time comes (I may be getting close to zero basis on a few which crashed so low during 2008 like XTEX, APL, EROC that I may have to research this soon - will see what my capital account is on the K-1s coming soon). There have been posts on the Investor Village board (especially those by Rock_n_Rent) which cover the subject in detail.