Subject says it all, how important is it to have perfect IV's. Can I get away with just having perfect to near perfect IV's in relevant stats or is it pretty much mandatory to have every state be perfect in order for a pokemon to be competitive.

Like for example if I had a Zekrom that had perfect Attack and speed IV's but the rest of the stats weren't perfect but most were at least decent would he still be a competitive worthy dude to bring (ignoring his viability in the current meta)?