As with putting, if you can't control where you hit the ball on the clubface you can never truly control your shot. It is a good idea to spot check your ball contact with your driver, midirons, wedge, and putter. Although you can see a general wear pattern on well-used clubs, if you are trying to change or improve the impact point you need a way to monitor the change.
These impact decals come as a roll of 250 labels for about half the cost per label of Red Dot-brand golf impact labels. The impact decal design is a 'universal' oval shape so they can be used on both irons and drivers. Cut them in thirds to use on your putter (cut vertically and you can get 3 putting decals per impact decal) or you can purchase actual putting decals on this site.
Spray chalk works well for indicating impact but many people find the decals more convenient to use, especially hitting irons where the chalk can come off in the grass. Although you can see the impact clearly on the first shot you should leave it on until you have established a pattern. If your impact is poor this might only be 4 or 5 shots. Snap a picture and monitor your progress over time. Better players can leave the decal on for 20+ shots and should only see a one inch black oval on the club's sweetspot.