The real constraints
Minimum draw amounts. A $5,000 minimum against a $900 need means borrowing five times what you want and paying for it.
Per-draw fees. A flat fee or a percentage on each draw turns a low rate into an expensive one for anyone drawing weekly.
Minimum interest periods. Some facilities charge a minimum of thirty days' interest per draw regardless of how quickly you repay, which removes the main advantage of the product for short gaps.
Availability. Repayments usually restore the limit immediately, but some providers take a day or two to clear before the funds are redrawable.
Using it well
Batch draws where you can. One draw covering a week of obligations usually costs less than five draws covering one day each.
Repay quickly and deliberately. On a daily-balance facility, repaying a fortnight early is a real saving, unlike on a fixed-factor product.
Keep some headroom. A line drawn to its limit offers no protection against the thing you actually needed protection from.
What providers watch
Permanent utilisation. A line that never returns toward zero is read as a term loan the business cannot repay, and it is a common trigger for a limit reduction at review.
Drawing immediately before a review, or immediately after an increase, attracts attention.
Account conduct generally. Because the facility is reviewed, how you run the account during the year determines what the limit is next year.