Hijacked straight from http://techniek.flipperwinkel.nl/wms11/index1.html

2d. Before Turning the Game On: Should I leave my Game Powered On?

This is a very common question. After all, arcades leave their games on almost continually with minimal damage (that you know of!). So why not do it with your game at home?

Although commercial pinball machines can handle being powered on continually, I would recommend you do not leave your games turned on when not in use. Here are some reasons:

• Electronic score displays on your game have a limited life, which is proportional to how much time they have been turned on.
• General illumination circuits will be stressed. Burnt pins and connectors are very common on games that are on for extended periods of time.
• Light bulbs don’t last forever, and aren’t all that easy to change on a playfield.
• The bulbs, displays, fans, and transformers only attract dirt when they are on. Leaving your game on means sucking dirt out of the air and depositing it into your machine.
• Heat generated by the general illumination lamps can warp playfield plastics or help delaminate backglass paint.
• Electricity is a precious resource. Conserve it! An electronic game from this era consumes about 4 amps in attract mode. So leaving your game on is like running a 240 watt light bulb. By comparison, an entire stereo system plus a television use about the same amount of power.

Leaving your pin on all the time can cost much more than any potential damage you could do turning it off and on as you need it.