You can make a TON of arguments against this and for this. It doesn't have an exact answer, but in my personal opinion:
If the person that is being fed on the enemy team is someone who can absolutely destroy your team by themselves (any champion can do this basically, but the ones that are REALLY GOOD at it like:
etc), Unless you are confident enough that you can make either yourself strong enough to take this person out in fights, or make someone else strong enough to do so, you need to gank said lane. You don't need to IGNORE ALL OTHER LANES, you just need to help out a bit.
HOWEVER if there is a high chance of getting doubled / tripled killed on, don't. It all comes to experience and what you think.
Its super situational in my opinion, sometimes the answer is no, sometimes its yes.
Another thing is if this enemy laner is pushed up and the kill is pretty much guaranteed, go for it, dont ignore the lane if you can easily shut said person down.
Because if this person is too big for your team to handle, then you may have lost yourself a game because you simply did not make the right decisions on who to help in your lanes. (although I know most people will say it can be blamed on the person who actually lost the lane in the first place, a jungler's response)
From mathmatic perspective, this would be like:
abc=xyz , but each game the (the given situation,)abc changes due to various factors, and the xyz (the correct/best call to make,) changes. abc=xyz can change to acd=yzx and so forth.
TLDR: It honestly depends on many factors so you must be intelligent as a jungler to gauge which option you choose, either ignore the lane completely, help it slightly, or focus on it.