How bad are bad sectors

The actual bad sectors are a property of the physical material in the drive, and are not copied. In other words, if you have ten bad sectors on hard drive A, and five on B, and you clone A onto B, B still has exactly the same five bad sectors that it did before the cloning process.

I would assume that the hard drive itself (or any checkdisk-style process run on the drive) will map those sectors elsewhere so that the cloning software doesn't try to write data to them, but that has no impact on the actual bad sectors present on the drive, and doesn't change the answer to your question.

You do have one problem, however. If the hard drive you're trying to clone has lots of bad sectors on it, then data may have already been lost. So you're probably better off reinstalling anyway, and moving your data over afterward.

First off, bad sectors will not be copied over.

Most of the time, programs that claim to fix bad sectors do not fix them. What they do is find out where the bad sectors are and put police ropes all around them to prevent your system from writing data to those blocks. Does is work all of the time?, no.

You should replace the disk. You risk your data by not replacing the disk.

Copy everything as soon as possible.

You can also try to do a full format on the hard drive (once you get as much data off as possible). Sometimes a full format will help clear up any bad sectors, but is more of a long shot.

Scanning the HDD continuously should not increase bad sectors, but got, it'd be annoying to keep scanning drives with bad sectors.

One thing i've done in the past with a bad disk (more motor related) with is plugged it in outside of the computer. I had a pan of some water and ice sitting on the drive (after having it in the freezer for a bit). I kept the drive extremely cold and was able to copy over data.