Either you need to cover up a logo you can't remove, or you need to relabel a product who's logo has been removed.
Either you've given up trying to remove the logo, and other more elegant hiding methods haven't worked, or you have succeeded in removing the logo, but now you run the risk of not knowing what was originally in the package.
Adhesive stickers are also useful for leaving messages around the house that can act as reminders to lead a less stressed life.
Using adhesive labels as a means of covering a logo is really not elegant. It's a lowest end tool for a lowest end method. If you find yourself having to cover logos with stickers, it's time to find another product next time you go shopping.
On the other hand, adhesive stickers are very useful when a logo encompasses all of the labeling on a product, and once the logo is removed, you run the risk of not knowing what was originally in the package. This can be the case with such products as spices (for those of us cooking-impared), shampoo, laundry detergent and cleaning supplies.
Remove sticker from it's paper and apply over offensive logo. You can color with a marker to have it fit in with the background of the product better. You don't have to use the entire sticker if the region you need to cover is smaller than the sticker. Likewise, multiple stickers can be used to cover larger areas.
In the case of the relabeling use of stickers, apply the sticker to the product you just removed the logo from, and write the generic name of the product on the label. Note that if the product is going to get wet, like a shampoo bottle, you will want to use waterproof ink on the label.
Stickers can be used to cover logos, but this is very gauche.
Stickers are also useful when removing logos to relabel the cleaned products.
Stickers are also useful for leaving reminders.
No special skills.
Any stationary store will carry adhesive labels. There are no special properties of labels I can think of.