Apps taking up too much space on my computer harddrive?

40GB!

I have 243 Apps that use 3.15GB of storage. So, as a very rough calculation, that suggests you have 3,085 Apps. If you don't have anywhere near that many, there's something wrong.

400 apps taking up 13.6Gb so I get an estimate of 1,175 (wow I have some bulky apps!) but 40Gb sounds like quite a haul.

A couple of things come to mind. First is that occasionally iTunes can neglect to delete the old copy when apps are updated so you could have some orphaned files in your Mobile Applications folder.

Second, your apps should be stored in the same location as your music and movies but I'm guessing from what you've written that they're not. This means you are likely to have a split library with the database and supporting files on your internal drive and media in another folder, but in the old school layout. Assuming you are happy letting iTunes organize your files (and you have a backup) using File > Library > Organize Library > Rearrange files in the folder <Media Folder>, followed by File > Library > Organize Library > Consolidate files will sort that out. You'll have to delete the now redundant copies of the apps on your internal drive. The good news is that this will have dealt with any orphaned apps.

In the long term you might want to consider making your library portable.

Note switching to iCloud backup should not remove any content from your computer. I suspect purchases still get transferred when syncing but I've not tested it.

tt2

iTunes backs up your apps in case you need to restore the device. When restoring application data is only restored if the app can also be put onto the device so having all the components to hand is a good thing, even if it takes up some room on your hard drive. Perhaps if you backup to the cloud then it might not be necessary to keep copies on your computer, but frankly I would not risk it.

There are pleny of apps that come in universal versions where one app can serve both iPhone and iPad so I would expect a degree of overlap. Compare the number of files in the Mobile Applications folder with the number listed in the Apps section of the library (this number will also include any older ClickWheel games you may have).

tt2

If you drag & drop content from your library to the device then you are manually managing it. If you are adjusting checkboxes then clicking the sync button in the lower right of the device display then you are syncing. There is an option under Edit > Preferences > Devices to prevent automatic sync on connect, but that's not the same as manually managing.

tt2

My apps take up 94Gb and I have barely any space left . I have loads of apps but I doubt that many. What do I do???

If I delete it all will it lose all the backups or something?