If you are playing more than an hour a day, you should oil every day or two. Oil is not just there to keep the valves moving easily, it also flushes contaminents away from the pistons. Damage/wear can happen long before our insensitive fingers notice something. Long valve oiling periods are not something to brag about. I would label them more as "dumb". Valve oil is MUCH cheaper than getting new valves. Alignment, if it is done right lasts much longer than 2 years. If you use felts, they should be examined yearly. If valve oil or water gets on the felt, it needs to be immediately replaced. No damage can occur, they just compress and that can make a big difference in how the horn plays.