In many matchups, many situations, it is useful to “bank” gold for a short period before breaking into upkeep. This is when you do not plan to straight up fight your opponent–you could be creeping, or harassing, etc.. It is differentiated from other banking situations in that it’s just for a short period for a little extra gold so that you can quickly produce your army and be ready for an encounter.

Examples:

• Single mine Human versus Elf; buy items, creep a little more, then break into upkeep and fight.
• Elf mirror; awhile back it was popular to stay under 50 for quite awhile.