If you need to generate large domain lists, domains will be generated in several chunks, so called Domain Blocks. Domain Blocks are very useful especially if you prefer to look at each generated domain.
E.g. you could set suitable Domain Block size (e.g. 100), generate domains and check their availability, popularity, etc. Then look at generated domains and if a desired domain name found, you won't generate remaining domains thus saving your Internet traffic or online time. If there are no suitable domain names in current Domain Block, simply delete all domains and generate another Domain Block using Generate Next Domains under Domains menu.