MP in relation to video output

I notice cameras are being advertised as 5mp with 1080p recording, just as a 3mp with also 1080p video playback.

If both have video playback/recording of 1080p whats the benefit of having higher Megapixels?

Also if they can record at 5mp why not advertise that res instead of the 1080p?

Appreciate any clarification on this.

Marketing decisions by cam companies can be a little confusing, apparently to the marketing people as well as the customer.

I'd guess that 1080p is a good trigger phrase, since everyone knows 1080p is good. However, there are cams that claim to have higher MP sensors but only support 1080p output, so you'd have to look closely at the specs to know for sure.

The specs should include a full set of resolution settings and the frame rates you can get at these settings. Deception and murkiness are common in the cam world, especially at the lower end, so buyer beware.

Assuming you can record at the higher MP settings, you can zoom in for more detail. If you can't record above 1080p, it doesn't matter much what the sensor resolution is in terms of real-world results.

In general, avoid no-name cams. If they're not a well-known company with a good website and good customer support, including firmware downloads, you're liable to regret saving a few bucks.