The phrase "rendering needless" implies that something is being done unnecessarily, and so antonyms for this phrase might include "essential," "necessary," or "vital." Other antonyms might include "important," "critical," or "indispensable." When something is rendering needless, it may also be considered redundant or extraneous, and so antonyms might also include "crucial," "sine qua non," or "mandatory." Finally, when thinking about antonyms for the phrase "rendering needless," it is important to remember that this phrase often implies that something is being done in excess, and so antonyms might also include "sparse," "bare bones," or "minimalistic.