Take whenever you want to.这个句子为什么要加to?

为了避免重复,在hope, wish, want, like, love, decide, plan, mean, prefer,WANT, have to, be able to, be going to, used to, ought to等动词及习语后面出现与上文相同的不定式时,常保留不定式符号to,而把其它部分省略.如:
ms king lied to us because she had to.

金女士跟我们撒了谎,因为她不得不这样做.
－i heard that you would go to dalian for your holiday.

我听说你要去大连度假.
－i planned to, but i have some important business to deal with.

我原计划去的,但有重要的事情要处理.
详细关于不定式TO的省略与保留,可参照：http://www.***.com/fp/column35652/747e59bc-6743-4abc-8cc5-8a6b87b427f5.html
希望采纳~~

want to是一个短语

这是一个从句，具体是宾语从句还是定语从句什么的我忘了，后面省略了动词，所以是必须要加To的

各语言自己的习惯嘛...

后面省略动词take。