Why is it important to wipe excess lubricant off your chain?
The primary purpose of chain lube is to lubricate the rollers and other internal parts of each link, not to lubricate the outside. Excess lube on the outside of the chain will get dirt stuck to it, that dirt will slowly work its way into the rollers that you're trying to protect, and dirt inside will grind away at the internal parts and wear out the chain faster.

I wouldn't use toilet-paper (WC-paper), as that's usually pretty flimsy and will leave bits of itself behind. You don't want to wipe with something that will leave anything behind. Use a lint-free rag of some sort.  I either use a worn out dish towel or a worn out sock. A sturdy paper towel would probably be fine.

I interpret "to wipe" as meaning to rub an absorbent cloth against all 4 sides of the entire length of the chain, such that there's only a thin coating of lubricant left behind (no visible drops).  I would usually wait a few minutes and ride the bike around to give the lube a chance to penetrate into the internal parts of the chain, then wipe off the outside of the chain.