On most pages, you can have a up to 21 blocks. See this limit as an invitation and an opportunity to organize your content more effectively for Google and for your readers. On each page, you should write on only one topic. Shorter, clearer pages invite your readers to continue exploring, either by clicking on a link on your page or on a menu tab.
Keeping pages short is also a way to make your website load faster. This improves the browsing experience for your visitors and the visibility of your website on Google. Don’t forget that most people use their mobile phones when they browse the web. Studies show that visitors often quit a site after 3 or 4 screen lengths if there is no call to action (e.g. a link to go to another page).
The exception is the Blog page, on which you can have up to 99 blocks. You can add up to 10 posts per day, display the date above each post and, on Smart and Pro sites, include a comments box below each block.
Note that there is no limitation on the length of the text you can type in a block, whatever the page type.