Why do speakers recommend amp wattage?

My Usher speakers recommend am amp with 80 watts per channel. Ive heard amp wattages differ significantly, so why bother with a recommended wattage? What would happen if I used 200 watt mono amps (obviously overkill), or a 7 watt tube amp? Thanks.
Probably a rough estimate of the power needed to drive the speaker to max. sound pressure level for extended periods of time over the full frequency band for most recorded music. Amps that are underpowered may not be able to produce enought power at peaks resulting in clipping and speaker damage.

A 200W amp will be okay, not much chance for speaker damage.

A 7w amp might be okay if you don't play very loud (but SETs are effected by so many other factors, so I would avoid using them unless you are really shure)
Probably because people expect it. In one sense it isn't very useful since size of room, average listening levels, type of music, ability of a given amp to driven a given load, as well as other factors play into how much power the amp should have. However, it gives you a general idea where to start. This is an area where there are so many variables that absolutes can't be given.

BTW that 80W is "power handling" which is different than recommended as it is the maximum they recommend. Probably the maximum continuous which is very different than the maximum peaks when playing music. Given their efficiency of 87 dB I think you would want an amp that is at least 80 watts and more wouldn't hurt.
You could put a kilowatt in front of your Ushers without fear as long as you were actually listening as you turned it up. Running at 'redline' for extended periods will probably result in some kind of meltdown, or ear damage!
Low power at too high a level is probably worse, as noted above.

Tradition, I suspect. Often, the impedence curve is more important.
Nice thread. I was also curious about the wattage.

What is the importance of "current" in amperes? I have seen specs of amps with wattage but different current output. For eg. one amp had 200 Watts per channel and gave 60 amperes where as another gave 200 Watts but 45 amperes.

The most practical reason is as a guideline to avoid distortion and speaker damage due to clipping by running an amp with too little power too loudly.

In general, solid state amplifiers that deliver more current (amps) are able to better drive most dynamic speaker designs with varying impedance curves at various frequencies (referred to as a "difficult" load)and deliver more balanced sound from low to high frequencies.
Duh. The more Watts listed on a speaker, the louder it is. That's why I only buy White Van speakers. They are always, like, 250 Watts and really rock the house. Way better than that Bose crap.
Instant current delivery is of some importance. Continuous? quite a bit less, since SS amps are typically voltage source amps.
Even my panels, which are considered 'current hogs' by all, have only a 4 amp fuse on the mid/hi driver. Even if the LF driver could sink another 4 amps, that is something like 400 watts.....50v x 8a. But still 'only' 8 amps. I have no idea what I'd do with 60 amps, other than open a welding shop. Could my panels do this on a continuous basis? Doubtful, not to mention ear damage.

As for Mapman's 1st sentence....Agreed! Advisory spec, at best.

As for Mapman's 2nd sentence...Please consider Power Factor....that measure of a speaker which is phase angle. PF=cosine of the phase angle. This means that a 45degree phase angle reduces available power by about 30%, right off the bat. If this hi phase angle occurs at 'hi energy' frequencies along with a nice impedance dip.....there you go! By the time you hit 60degrees, the power is down to 50% So that highly touted 300 watts is down to 150 while the amp continues to work just as hard. This is the reason that some speakers are notoriously 'bad' loads. Not simply low impedance, though that plays a big part, but that coupled with low PF will kill even a fairly robust amp.