Caution Shown in CrystalDisk Info  

Bree said:

If the drive was really failing the sectors would be reallocated and added to the Reallocated Sector Count, that one is a strong indication of imminent failure. If the sectors are tested and found to be good then the pending sector count is cleared as having been a 'false positive'. In that case the yellow warning will return to a blue 'healthy' indicator.

the part of "the yellow warning will return to a blue 'healthy' indicator" does not always happen to all hard drives from all manufacturers, Bree.
especially older HDDs made at least a decade ago
I've only seen that happen with most modern Western Digital and Seagate brand desktop HDDs

erpster4 said:

I've only seen that happen with most modern Western Digital and Seagate brand desktop HDDs

I have only seen the one example. That was a Toshiba 1TB which returned to being healthy, so you can add another brand to the list.

Pending Sector Count are sectors marked as potentially needing reallocation. A SATA drive should reset it to zero if subsequent tests show the sectors to be good. Of course, if they were correctly marked as bad they'll get reallocated, then the yellow flag will move to the Reallocated Sectors Count and the drive should be regarded as unsafe to use.