I’m just getting started and am going to buy some ball lock corny kegs. I see the option odf low profile kegs that are moer expensive. What’s the difference?
I do not keg (yet) but I have been looking into corny kegs. I believe that the low profile kegs are just slightly shorter and wider versions than the same gallon normal kegs. Just a small dimensional difference. Depending on where you plan on keeping your kegs, one style might be more practical than another.
Don’t quote me on this however. 
Pin lock kegs are shorter than ball lock. Is that what you are looking for?
I’ve seen ball lock kegs advertied that are more like the dimensions of pin locks. In fact it appears that many of the used ones are just converted pin locks. As Megary advised, decide what dimensions are ideal for your space, then shop around. There are various options in new and used kegs.
There are a small number of original low profile ball lock kegs but most of the low profile ball lock kegs you find on the market these days are rebuilt pin lock kegs. They are more expensive either because they are rare originals or conversions that cost money to convert.
Unless you have a specific need for low profile kegs there is no point in spending the money. Consider as well that there are low profile quick disconnects that can shave an inch or so off the height of your kegging system as well. They are a lot cheaper than sourcing low profile kegs.
And if height is the concern, this option (and if height is no concern it’s a non issue) has the added advantage that skinnier kegs saving floor space in your fridge/wherever could possibly mean more kegs, or room for a gas cylinder.