Pre-Computing segments allows you to minimise the delays resulting from the time taken to run complex segmentation queries, while sending the campaigns. It will ensure that your Push campaigns are sent at the designated time.
If you are using a complex segmentation query that usually takes a good amount of time to run then during campaign creation, on the Scheduling page (Step 3), select the check box "Compute target audience in advance to ensure that campaigns are sent faster and at the right time."
How it works:
In order to make sure that all intended reachable users are targeted, we fetch users from the segmentation right at the time of sending the campaign so that any potential customers are not missed.
But the downside is that if the segmentation query is complex, it can take upto 45-60 mins to run the query and fetch users. As a result, the campaign get stalled by the same amount of time as it cannot be sent until users are available.
Pre-Compute solves this problem by running the segmentation query in advance anytime between 30 mins to 2 hours. Hence, at the campaign send time, the target users are already available and campaign sending starts right away at the scheduled time without any delays.
Note: The only caveat here is that there is a small risk of losing out on the customers who didn't qualified earlier but qualified after the segmentation query was picked for pre-compute. Example - Lets say you want to target users who added product to the cart in last 24 hours and there are 5K users who qualify for this criteria when campaign was picked for pre-compute. However if 10 more users added the product to cart after that, these users won't be targeted by this campaign.
So, it really involves the trade-off between the timely delivery of a campaign vs the capturing all the intended users. Accordingly decide whether you want to go for computing users in advance or not.
Editing campaign when pre-compute is ON:
If the segmentation query of the campaign was edited 30 mins prior to the campaign sending time, then the list of users computed in advance will be dropped and the target users will be fetched at campaign sending time which could add up to potential delays in campaign sending time.