Complicated answer:
To answer it, you need more information
(1) What was your Step 1 (less than average, average, above average, stellar)?
(2) What are you applying to (competitive, not competitive)
Because if you were stellar on Step 1, you risk having an inferior score. Let the stellar score ride you into a residency interview. Then, you just pass Step 2 and call it a day. But if you are anything short of stellar, Step 2 can prove very useful.
In addition, 5 years ago Step 2 didnt matter. Now, programs are using it as marker of clinical success. It matters now. It not only can be used to boost a poor performance on Step 1 (a girl I know was specifically told she got her surgery interview because of her Step 2 score and would not have received that interview because of her step 1 score), but is now becoming more and more required by progams for acceptance.
Universally true is that Step 1 gets you the interview, and Step 2 can help with the rank list. It isn't a must, and having on ERAS is not essential. If you are going to do well on both, seal the deal and be all like "yeah, boss, rank me." If you did poorly on Step 1, use step 2 to show that it was a fluke and that you really are a good candidate. If you annhilated Step 1, and your program doesn't specifically mandate you have a Step 2 score in, take it late.
There is no universally true answer for Step 2 right now. In general, however, I would recommend having it on your ERAS. Treat it like Step 1. Its hard, important, and makes a difference on whether you get an interview or not, and, more importantly, where you end up on the rank list.
Obviously character, feel, interviews matter more, but don't give them a reason to decrease your rank because of Step scores (i.e. take it early and destroy it OR take it late enough for it not to matter)