Determinate tomatoes grow like a bush. Indeterminate tomatoes are viney meaning they grow almost exclusively from the tip if suckers are trimmed off. Because of this, trimming the growing tip of an indeterminate can severely reduce yields because it trims off the part where blossoms and fruit are produced. If the tip of an indeterminate is trimmed the suckers should be left to grow to form new tips capable of producing blossoms and fruit but it will take a lot longer. Ideally an indeterminate should just be staked and allowed to grow with only side shoots trimmed off. I mention this only because most articles fail to mention specifically not to trim the tops of indeterminates.