Bitcoin Forum

if I'm using a different client other than Bitcoin? I had Bitcoin lte installed previously, but now I'm using cgminer. Does that mean the app-data folder isn't necessary?

I'm a newbie too but I think the answer is "it depends".  First, if you delete the folder, you will loose the wallet that is there.  Are there any bitcoins in that wallet?  Also, which bitcoin address are your mining profits going to?  If that address is in that wallet (from the bitcoin-qt client), then you will loose all of your mined coins also.

Hopefully an experienced bitcoin user will correct or confirm what I said...

CGMiner is not the bitcoin client. It's a mining client, which allows you to connect to a pool and mine for bitcoins. There's a few more clients apart from the Bitcoin-qt client (downloaded from bitcoin.org) like Electrum, but it's a good practice to back up the wallet.dat file in appdata\bitcoin before deleting anything as that contains your coins.

If my coins are stored in an online wallet, like Mt Gox, does that mean those files don't contain anything important?

If your coins are at Mt Gox, then you should be fine to delete those files. However if you plan to ever use that particular wallet again you will need to back up the files prior to deleting.