You don't NEED to buy inventory space, there is more than ample as it is, you can buy more purely for convenience, unless you like to carry half your bank around with you then you won't need to buy more
I have to disagree. Bag/bank space and gem prices are currently my biggest issue with the game atm. I think it is practically impossible to play through level 80 without buying bank or bag space. Not everything used in crafting fits into the crafting tabs thereby forcing you to put things into the main bank space which is only 30 friggin slots! 30 is just a pathetic amount to start with and shows that they are obviously forcing the cash shop on a supposedly f2p game. What makes things worse is the trading post being down so people are trying to store things in the bank until the TP is back up when they can finally attempt to sell stuff. On top of all that, there is NO discount for bulk gem purchases??!! That's a double screw you by anet! Limited inventory space to start off with, plus no discount on bulk purchases even if you ARE willing to purchase that extra inventory space. This all just wreaks of a money grab scheme to me.