2 Answers

Actually, its better to learn this chord -- its a really good one.  Its also called a half-diminished chord, since all the triads are not minor.  I'll talk about how I use it and then get to your question. And of course the answer depends on the context -- the melody and the rest of the progression. 

I like to use them in minor keys as the "ii" in a ii-V-I.   For example,  Bm7b5, E7, Am

And in minor keys I'll sometimes use them instead of the v chord.  

And they make a nice transition between the I and ii chords in a major key. For example: C Dm7b5 Dm

But going the other direction, lets say we are in the key of Dm.  If you see a Em7b5, you might play a VII (C) or a V (A7) or even a iv (Gm).  But that really depends on how the melody tends to center.  You can figure out what notes are in the chord and in the melody and pick that way, or (even better) just listen and play what feels best.