My DSLR makes pictures with a 24Mpix 'resolution'. That's 6,000 x 4,000 pixels.
My computer monitor (is a bit old) but can only display 1024x768, or 0.76 Mega Pixies... newer ones maybe a few more but the latest generation of high-res monitors only offer up to about 4Mpix on screen.
Any more pixels I may have in the image I get out of the camera, are then going to be significantly 'wasted', by the time I come to look at them, and image re-sized to screen, either just dumping unneeded pixel data, or taking an 'average' of perhaps six image pixels to create a 'display' pixel.
As to printing? Gets more complicated here.
DPI is dots per inch. One dot does NOT equal one pixel. The printer puts down a dot that is normally pure 'black', 'Cyan','Yellow' or 'Magenta', colured ink. Ie the printer may have to may down five or six 'dots' per pixel to make the colour that pixel represents. More, to obtain the shading seen in an image, it will likely work on dot-density principle, laying down maybe a dozen dots of each ink to get the 'shade' over a wider area than the suggested dot-density, that no longer gives you a directly comparable 'resolution'.
Lets say, that the printer uses four ink dots to represent one pixel; that means that at an A4 piece of paper, aprox 8x10 iches, printed at 300DPI, could give you 7.7million dots, but that would only represent just under 2million image pixels... depending on the degree of interpolation to turn pixels into dots, and pack dots to get the same shading, likely a lot less.
So, you would need an incredibly high DPI printer, something that can lay down perhaps 2,400 Dots-Per-inch or more, or start looking at some more elevated technology like multi-layer thermionic printers, that can actually put different coloured dots on properly top of each other, and/or you would have to start trying to print out at very much larger paper sizes, before, like the computer monitor, you started to run out of 'pixels' you captured with the camera, you could show in the picture, on paper you look at.
Oh-Kay.... My first digital camera, over 15 years ago, offered just a 1.3Mega-Pixie sensor resolution. That was more than enough to be able to print 'acceptable quality' A4 prints on a desk-jet printer, and still more than enough to up-load a picture, that probably STILL has to be down-sized to under 1Mpix, for most web and screen -display purposes.
My 24Mpix DSLR gives me enormously more pixes to play with, but ultimately, very very few of them get looked at. In the maths a computer uses to make a display mage from whats taken by the camera, it does give a lot more cope to mess, and does mean that there's a much wider 'pool' of original data for t to 'iterpolate' f I decide to adjust the colour or contrast or anything. Also meas that I ca choose what the computer throws away before it does, taking a 'crop' from my captured image.
That significantly has relevance, when, with as with that little 1.3Mpx digital, it was suggested You don't need a 'zoom' lens, you an 'zoom' digitally..... which did't take two decades of evolution to deny the truth of... B-U-T holds some.... and I chose that 24Mpx DSLR to do just that, anticipating using a fish eye lens that masks 1/3 the sensor to make a round image, to begin with, and cropping a square out of that, wastes 1/3 the pixels left, rendering the out-put o my 24Mpxie sensor, something like, 10Mpix before I start messing more seriously....
To WIT the answer is, that more pixels MAY be 'better'... depends what you want to do. Does NOT automatically mean that having more mega-pixies automatically makes a picture 'better'.
I could take a 24Mpic photo of my foot... its hairy, smelly and probably as hygienic as it is photogenic..... that photo wouldn't be ANY better, because it had 24Mpixies, than if I had taken it with my phone, at its lowest setting to get something 800x600 or less than 0.5 Mega-Pix....
I could take a fantastic picture of my daughter, who is inordinately more photogenic than me, let alone my foot! And a 600x600 low-res phone-cam snap, would still be as worth while as something taken with my 24Mpix DSLR and a prime lens.. especially when down-sized to upload to web, and likely compressed by software by the host-site, to be seen on screen, on a PC or worse still, a smart-phone!
So much of the photo comes from looking THROUGH, not AT the camera, even less the specs for that camera in the manual!
Good photo's are take by good photographers.. and most of it is in the subject to start with..... a better photographer, with a better camera stands a better chance of taking a better photo, BUT, better is utterly subjective, and the hardware is the last thing to have influence on that, and the mega-pixie count only a tiny part even of that.....
So, ultimate conclusion is YES yo can have too many mega-pixies... they tend to take more proceeding power to handle, they ted to take more memory to store or display; not having so many to start with, you can get a camera to work faster, get more pictures on a memory card or hard drive; you can more readily open them and look at them, or edit them.. and unless you are going t get ANY real appreciable benefit from them n what you ultimately look at, they aren't helping you any making them in the first place.....
Otherwise, does it matter? If you can have them and it doesn't hurt any; they cant make the picture worse. BUT they very seldom might make the picture any better. And there's a heck of a lot, so much more worth worrying about.