For golfers of a certain vintage, they can vividly remember playing in a competition and having to ask a playing partner or opponent if they thought some damage on the green was caused by a ball or a spike mark. Under the old rules of golf, if it was determined a spike mark was to blame, the golfer couldn't repair the damage and were left at a disadvantage.
However, under the new Rules of Golf starting in 2019, golfers are now able to repair spike marks and a variety of more damage caused to greens than previously allowed.
Repairing spike marks
Under the new Rules of Golf, the definition of acceptable repairs to "damage on the putting green" has expanded to include all damage except aeration holes, natural surface imperfections or natural wear of the hole. That means ball marks, damage caused by golf shoes, indentations from a club or flagstick and animal damage now can be fixed.
The interesting facet of this change is that there's now an expectation that more professional players will fix increasing numbers of perceived damage on the greens. However, we haven't seen excessive repairs to this point.
The USGA and R&A made the decision to expand the allowed repairs because the putting surface is a unique place on the golf course, where players have an expectation of a fairly smooth surface to hit putts on the ground. Of course, humps and bumps on the greens are possible, and there's no way to predict how putts will react, but players at least have an opportunity now to create as smooth of a path as possible to the hole for their putts.