What’s the difference between XL capacity ink cartridges and normal standard ink cartridges?

Honestly, ink cartridges are a scam. They're too expensive, there's barely any ink in them, they never work and they run out quickly. The Epson EcoTank ET-2710 would be better. Instead of cartridges, the 2710 uses raw ink, that lasts 3x longer, for half the price. I have first-hand experience with this printer, and it's AMAZING.

XL (extra large) cartridges have more ink than "normal" ones.  Usually twice as much. An OEM XL cartridge for my printer is $13. EACH.  My printer uses 4 carts. I buy a set of 4 remanufactured XL carts for less than 1/2 the OEM price for the 1.

It IS true that inkjet printheads can clog from unuse.  If your printer does not auto-clean the heads, then do a manual clean about once a month. Read your printer guide for the "how to". 

I pray to didn't get a printer w/ all 3 colors in one cart & black in another one. If you did, don't mess around w/ rebuilt cartridges.  You'll be unhappy.

XLs have at least twice the ink for less than twice the price.

if you print enough, it is totally worth it.

read the specs for your particular need

You'll get more ink for the money with the XL cartridge.  It's kind of like buying in bulk as the price per ml of ink will be lower.  But you really should only buy ink cartridges if you're going to print often enough to use them up.  If you rarely print in order to not go through expensive ink too fast, the print heads will dry up and plug and the entire cartridge will be a waste (and it's a pain trying to dissolve the ink and get it printing again).  Inkjets are great for photo printing but you have to print often enough to make them worth it.  If you plan to print a lot of color documents or photos, you may wan to look into printers with ink reservoir tanks.  They're more expensive, but all you need to buy for ink is just bottles of ink, which are very cheap compared to cartridges with the print head built in.  But if you print rarely, you're better off with a laser printer.

The main difference between the two is actually the amount of ink in each cartridge. Standard ink cartridge contains less ink and is, therefore, less expensive than high yield cartridge. XL or high yield cartridge contains more ink and therefore can be used to print more pages at a better value per page

See if the boxes list the volume of ink in each

Get a laser printer if you're going to be printing mostly in black.  The initial costs are higher, but they pay for themselves quickly if you do a lot of printing or if you print in bursts (that is, you won't print anything for a month or 2 and then you'll need to make a few quick prints here and there).  The cartridges in a laser printer don't have shelf lives and they last a lot longer than any inkjet cartridge.  Inkjet cartridges are designed to fail (that is, your printer will claim that the cartridge is empty) after a certain amount of time, whether or not it's actually empty.  Use inkjet for color printing, but use laser printers for printing in black.

That being said, if you have a lot of printing to do, you might as well get the XL, since it can print out more pages before it needs to be replaced.  Printer manufacturers have gotten better about making sure you can't refill an ink cartridge and reuse it.  If you can't tell, I have a lot of hatred for inkjet printers and I feel that the business model behind them is a scam.  You used to be able to get an inkjet cartridge refilled for $5, but now they've been made to be inoperable if a 3rd party vendor refills them.  It's infuriating.