Optimized range function for angular

range.js

// Extended answer: http://stackoverflow.com/questions/11873570/angularjs-for-loop-with-numbers-ranges/17124017#17124017
// By caching the function result, it can become orders of magnitudes more efficient (depending on how big the range is)
// jsPerf: http://jsperf.com/memoizer-range/9

$scope.range = (function() {
	var cache = {};
	return function(min, max, step) {
		var isCacheUseful = (max - min) > 70;
		var cacheKey;

		if (isCacheUseful) {
			cacheKey = max + ',' + min + ',' + step;

			if (cache[cacheKey]) {
				return cache[cacheKey];
			}
		}

		var _range = [];
		step = step || 1;
		for (var i = min; i <= max; i += step) {
			_range.push(i);
		}

		if (isCacheUseful) {
			cache[cacheKey] = _range;
		}

		return _range;
	};
})();

I stumbled upon here from your SO answer, just a curious query, may I know why the range of 70 specifically ?
Thanks!