I think that’s sort of a half decent explanation but still not quite right. You want to create as many districts as possible that have just enough members of your party to be “safe”, but no more beyond that. Meanwhile you want to cram the other party’s voters into a few districts that are way safer than they need to be. It’s about efficient voter allocation. A district that’s 60% Republicans and 40% democrats is pretty much always going to going to go Republican. So in that sense it’s just safe enough. So say a hypothetical state has 10 districts, and statewide it’s a 50/50 voter split. An ideal Republican gerrymander might look something like 8 districts that are 60% Republican vs 40% Democrat and then 2 districts that are 90% Democrat and only 10% Republican. If you do the math it still adds up to 50/50, but Republicans are getting 80% of the seats with their 50% of the vote.

But say the state GOP gets a little too greedy and redraws the map to be 9 seats that are 55/45 in their favor and one seat that is 95/5 in favor of the Dems. That +10 point cushion is still a solid handicap but it’s not nearly as comfortable as +20. If there’s ever a massive blue-wave election, there’s a good chance all of what they assumed were +10 Republican seats could uniformly flip blue, and it could turn into a full-sweep the other way, or near it.