Not all Apple Macs have big disk drives and if you have had one for some time you might be running short of space. This is especially true of Macs with SSDs (solid state disks) and early MacBook Airs for example, only had 64GB SSDs. Even now entry level models only have 128GB. You can free up many gigabytes of disk space by moving the iTunes folder to another disk drive, such as an external unit.
Advertisers are always looking for better ways to sell you even more stuff than they did previously and one way in which they do this is to track your activities in an attempt to see what you are interested in. iTunes does this on the Apple Mac and the question is, do you want iTunes tracking your activities?