What are boosted feeds?
A boosted feed is a feed you've asked Inoreader to check every 10 minutes instead of on its automatic schedule. Boosting is a Pro feature, and the faster schedule applies to everyone who follows the feed.
Without a boost, Inoreader sets the schedule itself, as How often are feeds refreshed by default? explains: an active feed with a Pro or Team follower is checked at least once an hour, a feed with no article for 30 days once a day, and a feed silent for a year once a week.
What a boost changes
A boost sets the feed's update interval to 10 minutes while the feed keeps publishing. When a boosted feed has had no article in the last 30 days, it's checked hourly until it publishes again. The boost belongs to the feed, so your boost speeds the feed up for every reader who follows it.
Right-click a feed in the sidebar and choose Feed properties to see its Update interval on the About tab, with the boost icon next to it. A boosted feed shows 10m, and the icon's tooltip tells you when you boosted it. How do I boost a feed? has the steps.

A feed marked Real-time already receives its articles by push, so a boost adds little there, and Inoreader asks you to confirm before boosting one. With a rule that sends an email or a mobile notification, a boosted feed works as a fast alert.
Feeds that can't be boosted
Newsletter feeds and monitoring feeds have no boost icon, because they're Real-time already. Feeds that Inoreader slows down for publishing too much, and feeds from some publishers, can't be boosted. The message then reads "Boosting is disabled for this URL. The most common reason for this is a publisher restriction." Telegram channels that post rarely are checked every 3 hours, and a boost brings them to 10 minutes too.
Plans and limits
Boosted feeds are a Pro feature: Pro includes 100, Team plans share 500 or 1,000 across the team, and custom plans can add more. Your boosts are counted under Boosted feeds in Preferences > Billing and usage, where Increase limits adds more. When Pro ends, your boosts are kept but switched off, and they come back when Pro returns. Unfollowing a feed removes your boost on it.
Can't find an answer? Contact support