Starting fermentation low?

[WaltG]

So making this recipe...

https://beerandbrewing.com/smoked-chocolate-rye-stout-recipe/

It says to ferment at 63F for 2 days then up to 68F to finish. I'm using US-05 and usually just stay at 68. Whats the purpose of starting lower?

 

[RM-MN]

By starting fermentation cooler you tend to get fewer esters for a cleaner taste. It also limits how fast the yeast work so there is no blow-off or runaway temperature. If you can control the temperature of the fermenting beer to just 68 degrees it will probably be fine but cooler might be a little cleaner flavor.