The sentence can be interpreted two ways if you do not understand the context. It could be understood as meaning "Do not use software compression or encryption of any type hardware or software" or it could mean "Do not use software compression or software encryption but hardware encryption and compression is OK"
You need to understand the context of that statement to get it's meaning and then you need to look at the environment as a whole to see the extent of the impact of the sentence. Remember Symantec is a software company (appliances not withstanding) so they focus on software and its affects.
You can turn on compression and encryption in your policies and when you do you greatly affect the performance of the client. In some cases up to a 25% performance hit during the backup. This is the type of thing that Symantec was warning about since GRT is a software function. So you are safe to assume that the sentence refers to software compression and software encryption.
That being said the paragraph is referring to the performance of the job and if you do not have enough processor and memory in the client performance will degrade drastically on the whole client. However, if you throw in hardware compression and hardware encryption you will degrade throughput but not noticeably.
Disk compression such as in NTFS volume can affect read speeds. Even frame side compression can affect read speeds but you may not notice it. Encryption at the target like an LTO 4 or 5 drive takes a write performance hit on throughput but again not as noticeable.
If you are worried about throughput for your GRT backups turn off NetBackup compression and encryption so as to not affect client performance, backup to disk, copy to tape, and then expire the image on disk. Always faster disk to disk and if you need tape the backup job does not notice the tape copy.
