Depending on your account plan, when adding a target you may have two different options to choose from: unlimited scans (available on Pro and Enterprise plans) or scans that consume credits (available on all plans). Your choice will depend on how frequently you run scans on your target:
If you scan your target frequently, you'll probably want to configure it so that it has unlimited scans; this way, you can run as many scans as you want, at no extra cost.
On the other hand, if you only scan your target occasionally, you may prefer to configure it in such a way that it consumes credits for each scan instead.
Learn more about credits usage here.
Configure Unlimited Scans/Credits for a Target
When adding a target, if your plan allows it, you can set it up as either having unlimited scans or as consuming credits. Later on, if you want, you can change this configuration.
In order to update your target's settings regarding unlimited scans/credits, you just need to go to your Targets list, select the targets you want to update and click on the button that appears on the actions list:
SET AS UNLIMITED or
If you set one or more targets as Unlimited, you can run as many scans as you want on those targets, at no extra cost.
If you set one or more targets as using Credits, each scan you run on those targets will spend credits.
Bear in mind, however, that there's a limit to the number of times you can switch these settings!