There may be two reasons not to over do power. Number one is big power costs more. and at a price point may use cheaper parts/ sound quality s less. (THis is not to say the particular amp is such. just a hypothetical)
The second reason is friends. drunken fools, idiots children etc.. a really powerful amp can kill a small speaker instantly, if it is cranked up far beyond the max power handling of the speaker coils.
THis could happen in many ways at a party, some kid, a sort or some flaw of signal before amp that send the killer 100% signal through the amp regardless of the volume control position.
So yes there IS a reason not to use an overkill amp.
But if you are aware of these problems, and guard against the obvious ones. should be OK.
Just be aware such problems exist if using a too big amp