Hey! It def depends on personal preference but we try to keep ours open the maximum (2 years). 

I like doing 1 year, so that guests who enjoyed their stay can rebook for next year. Make sure to increase next year’s prices (I use a setting in price labs to do this), so you can account for inflation.

I typically leave mine open for 12 months out. Although this totally varies, depending on market, some people do like to book that far in advance. 
 

I've never really seen a downside of doing this, outside of making sure that you're keeping on top of your pricing.